Regarding FBA (GCW), I've found that most games I've tried run perfectly.
Then we have Metal Slug. The first in the series runs fine, with a bit of slowdowns here and there, but nothing major.
Metal Slug 2 is another story. When the screen is really busy, with lots of enemies or heavy parallaxed background, the game lags a lot. This is especially noticeable on some boss fights, where the huge size of the sprites take a toll on performance.
On FBA A320 the issues are worse.