Cache makes a HUGE difference for mame... You notice it when you go down to a celery (wich has 1/2 the cache)... But I have one and its great.
But take note. The latest Intel cores (m2 something) are much better for mame then AMD's... and much better then their old processors per clock cycle... plus they are even more overclockable then AMD's.
This, but the way, is from reading the mame forum. I have an Operteron and have been very happy with it. But if I was going to buy a processor for my mame cab, it would be intel