i5 vs i7 and HT (hyperthreading) or not HT.
I'm no expert but have read that games do not utilize HT...yet.
But also read that this is a misconseption.
If u just gonna game then perhaps check into it to save some bucks.

There are many options out there, but really the real two key areas are a fast quad (or more) core and a card with 2GB vram or more.

2GB Vram is going to quickly be the standard if it's not already. This game, The Witcher 2 and Crysis 2 with the high resolution texture pack all require immense amounts of vram at their highest settings.
I can't run any of these games well (at 1900x1200) with texture detail set to highest. They all lag.

So whatever you do, try buy a card with 2GB+ of vram.

best thing to do, is to get onto the various game forums and see which are having problems with what hardware and also the sites which exist soley for hardware, such as Extreme Systems or Guru3d and formulate your path from there.