Hm, well it all compiles fine on my Uno.
Using the bench example in the SDFat library, my Transcend card writes at 62 KB/sec. I threw a 256MB SanDisk card in and there was a slight difference. It wrote at 234 KB/sec!!!
I guess I'll try my app wit this SanDisk card.
Still, I would like to transition to this SDFat library, I just have to figure out why the code won't compile when "Sanguino" is selected as the board type.