I can't really answer your question, but we just got our 300 and the meager amount of built in memory is enough for topo maps covering the entire state and our GPX file with 500 caches in it which still leaves over 50% of the memory free. Keep in mind we don't live in the most dense state around and only have topo maps loaded, so your mileage may vary...
-Robert
You can load more than 500 caches if you want to, right? And place topo maps on the sd card? It would be great if you could place all your data and access it on the SD card.
Yup, it will go up to 2000 caches with the 2.40 version of the firmware and you can load the maps on the SD card like you said. For my needs I haven't had to bother with the SD card yet.
I thought about the 400t as well, but decided that the 4.5GB of capacity (512MB builtin and 4GB SD Card) would be enough...
-Robert