Comparing notes, then:
i3-2100 (desktop?) - i5-2500k (desktop) - i5-2430m (laptop)
131.98% - 203.66% - 107.08%
146.24% - 208.21% - 150.04%
Didn't have a benchmark for Pong to compare notes on.
So, looking this over, it looks like that i3 is slightly better than a stock clocked i5 laptop chip. Yeah, I'm thinking that the question of i3/i5 depends on what all you're running. If you're 100% sure you're never going to need the extra CPU, go ahead and go with the i3, but with the advancement of emulation as it always has been, I don't consider that a safe bet at all.
Try checking the MAME manual at http://docs.mamedev.org