To expand on a previous post, my Transcend 133x 8gb card card was extremely slow (many times saw the message "card busy") and almost every game had graphical or sound glitches. Tried several formatting tools and eventually rendered it unusable to the Powerpak, now I get the "cart format error, use Fat16 or Fat32" even though the card works fine with any PC. Also get the same error on my NES Powerpak with this card.
Currently using SanDisk Ultra II 4gb (15mb/s) and SanDisk Ultra 4gb (30mb/s) with no problems yet, both of these cards also work on the NES version.