I have a 7200 rpm in my slim and haven't had any trouble. The FAQ on playstation.com clearly states 7200 rpm doesn't help with anything though, so it's not worth paying more for.
It does though. There's several tests you can find on the internet where games installed around 10% faster, and games run from the hdd rather than a blu-ray disk had shorter load times.
For example, the PSN downloadable version of GTA V has longer load times, more pop-ins, and lower FPS, but a faster hard drive fixes this issue.