If you want to game and overclock, skip the quad core. Go with the best C2D you can afford.
Games generally only use 1 core. Heat is a big issue with OCing. 4 cores make 4x the heat. Ergo, you can over clock
more with a dual core chip due to less heat.
Additionally, you specifically state you want to overclock, but I don't see an aftermarket heatsink anywhere. Intel's heat sink will keep your CPU from melting at stock, but I wouldn't trust it much more than that.
On my core i7, the stock heatsink at stock speeds was about 40 idle and 70 under load. Over clocked from 2.66 to 3.2 it jumped to 50/90. That's "bad".
I slapped on my TRUE120 and my temps went to 28 idle and 49 load.
The TRUE is pretty much the top of the line in air cooling. Don't get the copper. It's more expensive, HEAVY, and not much better than the standard. Only get the TRUE Black if you like black, there's really no difference.
Go with this HDD:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136319&Tpk=WD6401AALS
It's a 640GB. It's more than twice the size of yours and performs almost on par with raptor drives (not velociraptors).
Last week newegg had 9800GTX2s on sale for
LESS than the 9800GTX. I almost got one, but I'm just going to go to a 295 at some point. Look for the 9800GTX. You should still be able to find them for about the same price. However, why not just go with a GTX 260 core 216 for about the same price?
Newegg is generally pretty good, but NCIXUS.com can really whoop them on video cards and monitors. Same card, $40 cheaper:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136319&Tpk=WD6401AALS
Or, you can go with this card for $50 more that will absolutely sodomize the 9800:
http://www.ncixus.com/products/?sku=36241&promoid=1001&vpn=896-P3-1255-A1&manufacture=eVGA
But what do I know?