I use the 2Gb cards.
The 'only' probelm I've had once - the GPS did not 'see' the card at some time during the day - previously ok. I took the card out and put it back in .. gps now sees the card. !@#$$# ... Later when downloading the tracks .. some were mssing .. took the card out of the GPS and put it in a card read - all tracks now avalible.
Whatever you do - take more than one card with the maps on it .. T4A is less than 100Mb, take Island Oafs Morrotopo too .. still less than 100Mb IIRC ..
Daily logs are fairly small .. say 300kb each day (set on most) ... or less depending on how much you do in a day.
Regards Frank Warner
motorcycles BMW R80 G/S 1981, BMW K11LT 1993, BMW K75 G/S