I e-mailed edirol about the handling of a 4 gig card and got this response
The R-1 has not been tested with 4GB flash cards, but it should work as we
use FAT32 file format. We just haven't tested it yet, because a 4GB card is
as much as the R-1.
I'm assuming they haven't tested it out because 24 bit wav has a 2 gig limit anyways..
and 4 gig cards are still pretty pricey..
-matt