I believe the limit is 32GB as it is a MMC/SDHC slot. Anything higher than 32GB would require new hardware to accomodate SDXC. Also, I haven't benchmarked it yet, but I use a 32GB Class 10 in my pocket edge, and it works dandy, although I can't tell if it's full speed on the bus the edge uses as the edge can't play HD video that I want to stream from it =( So I wouldn't bother with anything over class 2 unless you have something higher laying around like I did