> You could also try a mame version optimized for amd ( 0.120u4 latest build). It gives > an increase in more demanding games
Actually it's more likely to help with the less demanding games.
CPU optimized builds are highly overrated. You'll see less than a 10FPS increase which for the most part will not be enough to make "more demanding games" playable anyway.
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.