All DS games work 100% with no lag. This is expecting that you have fast mini/micro/SD media 60X or higher. No complaints about the SuperCard DS support as its top notch.
GBA is a different story as every GBA game I have tried has slowdown or the graphics blur in and out: Mario and Luigi SuperStar Saga, GTA, all the Super Mario Advance Series, Metroid, Kingdom Hearts and a few more. I mean ALL the big releases don't work right or have major slowdown with more then 1 person on the screen!
FifthE1ement