> Besides buying a Core 2 Duo E8600 (still the fastest CPU for MAME AFAIK) the best > thing you can do for speed is using 64-bit MAME. That'll get you up to 20% speed > increase in some games, such as Namcos Prop Cycle, games that run on the ST-V > platform and a handful others.
Some searching reveals that there were "Extreme" versions of the Core 2 Duo processor at one point. According to cpubenchmark.net (which can give a very rough indication of performance) the fastest of these were more than 50% faster than Core 2 Duo E8600.