Anandtech:

At the end of the day I’d say it’s safe to assume the current crop of high-end ultra mobile devices can deliver GPU performance similar to that of mid to high-end GPUs from 2006. The caveat there is that we have to be talking about performance in workloads that don’t have the same memory bandwidth demands as the games from that same era. While compute power has definitely kept up (as has memory capacity), memory bandwidth is no where near as good as it was on even low end to mainstream cards from that time period.

The iPad 4 impresses; the Surface RT has a lot of work to do.