That's a really tough call, I think with those 2 machines it's like splitting hairs. Either one of those rigs, along with a mid-low range graphics card will run Supermodel with no problems at all. There would only be a few MAME games I can think of that would even come close to pushing those CPUs to their limits.......NFL Blitz, Gauntlet Legends/Dark Legacy, San Francisco Rush/California Speed. I'm sure there are more but these are the only games Im aware of that currently work but take a powerhouse of a system to run fullspeed. So with that said I think I would go with the 2nd gen i-7 just because of the slightly higher clock speed.
Either way you can't go wrong. It's like saying I want to drive fast, should I buy a Ferrari or a Lamborghini?