Unfrotunatelly FOSS driver pm capabilies are light-years behind catalyst. If powertop numbers from 2 mobile chipsets (radeon 4330 and 5650) are in any way meaningfull, going from high to low profile on idle/low load saves about 2watts, going from radeon low profile to catalysts gives another 5W. Also the problem is not just battery life, heat is even ore important. Fryning +1000$ laptop is way uncool. (pun kinda intended).
If you can overheat the laptop just by running gpu-intensive applications then it's either badly engineered or has dirty fans. Either way, I'd suggest not buying consumer level crap in the future.