ADDITIONAL PERFORMANCE INFORMATION
If people want to write up anything on performance of individual games (ie [insert game] has terrible framerate / audio glitches / etc") I can add them here for reference. Just post in the thread and I'll occasionally update this post.
**Some general notes** - 360 emulation on the X1 has V-Sync enforced, while the 360 often does not. This can sometimes result in higher framerate on the 360, but at the expense of screen tearing. The inverse of that is, the X1 will make the game run more smoothly, but sometimes at the expense of framerate.
CPU-intensive processes (scenarios where a lot of AI characters are interacting - combat scenes, heavily populated towns, etc) often wind up performing better in terms of framerate on the 360, while GPU intensive processes (cutscenes, areas where AI characters are not as present) wind up performing better on the X1. The preceding comments especially seem to be true on Unreal Engine 3 games, but again this is not a "rule." Just a trend among some of the more in-depth tests that have been run on sites like Digital Foundry and Eurogamer. Also note that when played on XBox One X, performance is almost always noticeably improved over both 360 and X1, even if it's not specifically enhanced for X1X.
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Alan Wake
Framerate/smoothness is as good or better than the 360, but there are some issues with crushed blacks that the 360 does not present. This can make some areas of the game difficult to navigate as everything is "too dark." Adjusting your brightness/contrast can help alleviate this problem somewhat.
Alan Wake's American Nightmare
Framerate/smoothness is as good or better than the 360, but there are some issues with crushed blacks that the 360 does not present. This can make some areas of the game difficult to navigate as everything is "too dark." Adjusting your brightness/contrast can help alleviate this problem somewhat.
Banjo-Kazooie: Nuts & Bolts
Framerate, especially when involving longer draw distances, can run into some issues no present on the 360.
Bayonetta
Very similar to 360 performance graphically. Eliminates screen tearing. Very slight input lag compared to 360 version.
Bioshock
Significant improvement on X1 if you unlock the framerate in the options menu. Doing so results in frequent 60 FPS gameplay.
Bioshock 2
Slight improvement on X1. Not as impressive as playing Bioshock 1 on X1.
Call of Duty 2
Improved on X1. Double frame buffer that was used when playing on 360 would cause the framerate to temporarily lock at 30 when the system became taxed, while the framerate on X1 is a near constant 60fps.
Call of Duty: Black Ops
Improved on X1. Generally smoother performance than on the 360.
Call of Duty: Ghosts
Improved on X1. More consistent 60 FPS. Funny enough, it's also a more stable framerate than the X1 version of the game (which obviously has better overall graphics than the 360 version) - so from a pure performance perspective, playing the 360 version on the X1 is your best option. Video here: https://www.youtube.com/watch?v=bnztSP2ojoE
Call of Duty: Modern Warfare 3
Improved on X1. More consistent 60 FPS on X1, locked 60 FPS on X1X.
Condemned: Criminal Origins
Framerate on the X1 is actually higher than the 360, but uneven, which can cause minor judder. The 360 version is usually judder-free topping out at 30 fps, but also has framerate dips that the X1 does not.
Crysis 3
Frame rate is better on X1 (and even better than that on X1X), but frame pacing is still a problem - eg, X1X usually runs at 31-32 fps.
Dark Souls
Crushed blacks, similar to the Alan Wake titles. Per Eurogamer's testing, "Frame-pacing is also noticeably worse, meaning that 30fps areas often see 16, 33 or 50ms updates, as opposed to the mostly flat, more pleasingly consistent 33ms seen on Xbox 360."
NOTE FOR XBOX ONE X: Framerate is improved across the board when playing on XBox One X, although the game is not specifically enhanced for the console and is still not a locked 30 FPS.
Dragon Age Origins
Generally more stable framerate than the 360.
Fallout 3
Improved on X1. Generally smoother performance than on the 360.
Gears of War
Improved on X1. Generally smoother performance than on the 360.
Far Cry 3
Improved on X1. Significantly more stable 30 fps than the 360 version.
Gears of War 3
UPDATED October 2016 - Recent patch noticeably improves performance. Previously had framerate drops, especially in horde mode.
Gears of War: Judgement
UPDATED October 2016 - Recent patch noticeably improves performance. Previously had significant framerate drops throughout.
Grand Theft Auto IV & Grand Theft Auto: Episodes From Liberty City
UPDATED - patch improves issues, game is now very close to 360 performance - usually has slightly higher framerate than 360. Prior to patch, frame pacing issues could give the game a "stuttering" look.
Halo Reach
UPDATED October 2016 - Recent patch vastly improves what was horrible performance. Game is very playable now, only minor, infrequent slowdown in some spots in multiplayer, with improved singleplayer framerate over the 360 version.
Hydro Thunder
Improved on X1. Generally smoother performance than on the 360.
Kingdoms of Amalur: Reckoning
Improved on X1. Generally smoother performance than on the 360. Locked 60 fps on X1X.
Mafia II
Improved on X1. Much closer to locked 30 fps on X1, only dipping during heavy action. Solid locked 30 fps on X1X.
Mass Effect
(Updates improved performance after initial back compatibility release). Cutscenes often exhibit better performance, while combat scenes still show some significant framerate dips - which is consistent with the original 360 release, so performance is accurate. However, on Xbox One X, the framerate is more stable during combat scenes, making X1X the easy best choice if you have it.
Metal Gear Rising Revengeance
Improved on X1. Generally more stable 60 fps performance than on the 360.
Mirror's Edge
Improved overall performance on X1, but some flickering can occur.
Pinball FX
Although most tables appear to perform well, there can be framerate drops at times with certain tables. Most notably, the table "Agents" will start off fine, but after several minutes of play you'll begin to experience frame drops, which in a pinball game is a severe hindrance. Similar, less extreme issues were noticed in the "Buccaneer" table. A small amount of the FX1 tables carry over to the X1 version of FX2 (see info
here). If you are looking to play the FX1 only tables, it's best to just play on the 360 if available.
Rage
Noticable audio issues. Some users reporting crashes to dashboard as well.
Red Dead Redemption
Improved on X1. Generally smoother performance than on the 360.
Saints Row
Improved on X1. Consistent 30 fps on both X1 / X1X where drops occurred on the 360.
Sonic The Hedgehog
Very slight input lag when compared to playing on the 360. (possibly due to enforced V sync on X1)
Sonic The Hedgehog 2
Very slight input lag when compared to playing on the 360. (possibly due to enforced V sync on X1)
Sonic The Hedgehog 3
Very slight input lag when compared to playing on the 360 (possibly due to enforced V sync on X1)
Star Wars: The Force Unleashed
Usually fine, but after playing the game for a while an issue can occur where the game begins to gradually slow down to the point of unplayability. Exiting and relaunching the game resolves the issue. This does not appear to occur on the X1X due to the graphics/performance enhancements.
Tom Clancy’s Rainbow Six Vegas
More noticable framerate dips than the 360, especially during heavy combat.
Tom Clancy's Splinter Cell: Double Agent
X1 holds close to 30 fps, with occasional dips into the low 20s. X1X is near constant 30fps, with only rare dips into the mid 20s. Both are significant upgrades over the 360, which can drop into the low teens on some occasions.
Trials HD
Performance is fine, but online replays are broken.
Viva Pinata
Although it doesn't reach the temporary framerate highs of playing it on the 360, the VSync actually causes the experience to come off more smoothly on the X1. Occasional slowdown during cutscenes, but gameplay itself is as good as the 360.