I did the dd benchmarks that we had back when SD cards weren't faster than the slots they were going in. Everyone was trying to find the fastest SD cards so several of us were benching them. Although the dd benchmarks would show similar performance results for EXT4 as EXT2, actual in-application performance on EXT4 was MUCH slower for me than EXT2 was. That may have been card dependent - hard to tell. Regardless, I think that it should be possible to do some basic testing of different FS formats to find out what performs best on the particular NAND that gets used in the Pyra - whatever that winds up being.