I have experienced lags in ak2.1 with 3 different microsd cards:
8gb silicon power class4
4gb transcend class6
2gb kingston
in both suikoden tierkreis and phantasy star 0, videos lag.
audio finishes earlier than video in a manner unlike the originals.
Some games may present small "gaps" where action stops for a split second when the game loads something from cart during gameplay. In my case I tried Kim Possible Kimmunicator. didn't like game, but in any case, during gameplay, in the lower screen, theres a menu that displays some "live" info, like messages and tips, and seems like they are loaded live from cart. Each time a new one is displayed, the game locks for a split second cuasing "stutter".
The fun fact is I have a friend with a DSTT and the same card (2gb kingston), and in his case, the video in suikoden tierkreis suffers from audio lag instead, or maybe it's the video that plays too fast. however it may be, the video finishes early and the audio is cut off :|