There is a thread in the German board where flash games are collected and rated as follows
(Grüner Status) ==> runs flawlessly
(Schwarzer Status) ==> a bit laggy, get stuck sometimes but rather playable
(Roter Status) => only runs with modified option, please state modifications
http://forum.gp2x.de/viewtopic.php?f=39&t=7127&p=86279&hilit=flash&sid=6d821e3c6a6cb861782f7e693eb41ae8#p86279
Most of the posted games are rated green, so probably it's not necessary to translate all the German text around the links - just try them out.
Kasi