Class 10 uSD card is slower than class 6 with SdFat library?

I'm using the SdFat library from Bill Gre...(i forget) and it is working nicely. I got a class 10 Patriot 4 GB uSDHC card to see if it would decrease the write time as opposed to my Transcend class 6 1 GB uSD card, but it certainly does not. When formatted as FAT32 like it should be, the library gives me all sorts of errors. When I format it as FAT16, it takes 4 times as long as the class 6 card.
Any thoughts?

The class of a card has little to do with speed on an Arduino. A class 10 card is optimized for large multi-block writes in 4-bit wide SD mode.

The Arduino uses single block writes in SPI mode. The speed depends on how the SPI controller is implemented. Class 10 cards only have a minimal SPI controller since SPI mode is required by the SD spec but is not expected to be used in high speed cards.

There’s always more to it than I think… Thank you very much!