i5 is the best buy of the iX series, as the hyperthreading of the i7 is likely of no use to MAME (or most other common applications for that matter) and the clock speeds are basically the same. i5 systems typically out perform identical i3 systems in PC game FPS by 20-30% according to most reviews and benchmarks, but like the previous poster commented, for MAME you'd probably notice little difference... For SSFIV you probably wanna get a discrete video card as opposed to onboard+lucidlogix virtu. With boxing week sales, i5+6950 costs about $400 here in Canada.
I assume c2d means Core 2 Duo?