I went from a 2GB class 2 MicroSD to a 16GB class 6 MicroSDHC; Rockbox performs the same with both, but it's a lot quicker when I copy large chunks of music to the class 6 16GB card. I have a slimline MicroSDHC reader attached as a dongle to my e280v1, just for the geek factor.

I did notice that since the e200v2 still has to connect using the OFW, my 16GB card causes some issues when I plug into my computer. The reader really comes in handy then. For simplicity's sake, I'm sticking with my v1 at the moment. In the future, I'll switch.