The regular HD3000 clocks at 650MHz, and can turbo boost up to 1300 when the thermals of the rest of the processor allow it. The low voltage variant has a standard clock of 350MHz, and can boost up to 1200.
Most single-run benchmarks I've seen show the MBA and MBP having similar GPU scores, meaning its likely they spend most of the benchmark time in turbo mode (otherwise the delta would be bigger between them, 350-650 is a bigger difference than 1200-1300).
That begs the question: After a while of gaming or other intense work, will the performance of the Air (or even Pro) drop off as it can no longer get thermal headroom to boost the GPU in? Can someone with either one run a looped benchmark and report the score each time? ie run one, 5000, run two, 4900, etc? I'm curious, I'm sure others are too.