8GB memory stick with W850i

I ended up with an 8GB memory stick for my W850i (long story) which seemed to be working fine (except only showing 4 gb is normal from what I read). However I think after using 4 gb all my files seemed to disappaer????? It's almost like it formatted itself. So I suppose I have a few questions:
1. Can I get my files back?
2. Should I downgrade to 4GB?

Thanks
Jeremy

I wouldnt have the same one as you... besides the slow access time, you can run a file recovery program on it when connected via usb. It should locate any lost or corrupted files.