should i buy a core i7 920 with i Gb ddr2 nvedia gpu or core i5 higher versions like i5 680 or 750 with 512 MB DDR3 gpu or the basic core i5 system with a 1 Gb ddr3 memory. my main purpose is none other than pC gaming . please help me out . for gaming does the difference i5 and i7 matter a lot