That depends completely on the process. IF it's 65nm, which I would expect it to be, then that's perfectly reasonable for a handheld part. Certainly it's in the upper range, but believable and okay from a perf/watt POV.
An ARM representative characterized Mali200's power consumption at about 0.9mW/1MHz, so a 300 MHz GPU in a mobile phone might be acceptable with a very good battery.