Read my posts in the mame thread new mame versions will not run most roms smooth on low speed cpu's whereas older mame versions should run smooth..
The reason i chose mame4all from the gp2x wiz is that it would be much easier to port than the same version from the official mame source.

Google it and you will find discussions on why new mame versions need medium to high end pc's to run most games smooth and older mame versions run most of their rom list smooth on average pc's.
People want quality performance from games not jerky, stuttering games which you have to turn the sound off to play.

FBA is great and works surprisingly well on my N900 but check the rom list its missing a lot of classic roms. Its nobody's fault its just what FBA supports.