First all your apps are stored on the phones memory. You have to hack store apps on a SD
If you copy the contents of one card to another everything should be ok. It's always good to do a back up first.
I switched from a Class4 from the Class2 and I think it loads faster but I could just be in my head
When you connect the phone to a PC it will only show the SD card. It was weird for me to coming from the WinMo but I'm loving it so far!