I also remember reading an article on Anandtech (famous hardcore hardware review site) about comparisons of write speeds. The quoted speed class is sustained write ie writing a single large file contiguously so a 10 beats a 4 in those cases. However, in Android, the majority of write activity is random small writes of 4k to 512k. In this area, performance of both class 4 and class 10 are almost equal.

And furthermore some forumer posted yesterday about the class 10 having fairly cacat speed. I asked for a second opinion but haven't gotten any one else's reply yet.

Anyway, I'm also holding out for a little price reduction before getting a 64Gb, and I'll still be reading up to see what happens.

YMMV.