I have a 60CSx and don't believe it supports the microSDHC (high capacity) format as it wasn't in use when the unit was designed and first sold. When I bought my handheld last year 1 gig was the largest capacity card available at the time with 2 gigs coming out at the end of the year. I have City Nav, Topo West and National Parks West for California, Arizona and Nevada loaded onto a 1 gig card, total memory used is about 350 megs. This leaves a lot of extra space for waypoint and route storage. I'm not entirely certain of this, but it seems to me that the more data you try to load onto the cards the more you'll delay your access times. At the level I'm using I don't notice any problems other than a minor system hang from time to time.