GPU upgrading advice please

[dagens24]

Hello all, I'd like to upgrade my GPU but I have a few questions for you all. First of all, this is my build atm.

Core i7 920
12 GB DDR3 ram
Radeon HD 4850
450w power supply

If I were to upgrade to a newer card (let's say HD 6950 or HD 6870 (which is better?)) would I have to upgrade my power supply as well? Would this new card emit a significant larger amount of heat? My case doesn't exactly have great air flow. Thanks for any insight all.

I realize upgrade the GPU, power supply and case would be ideal, but that turns a simple GPU upgrade into a HUGE system upgrade. $300 becomes a $700 :S

 

[Supernova1138]

The HD 4000 series was infamous for running quite hot, any current nvidia or AMD card will actually run cooler than your 4850, the dual GPU cards being the possible exception. The 6950 is the better card of the two you listed. It is about 12 to 15% faster than the 6870. The 6950 is a larger jump over your 4850, so you may want to go for that. For a 6870 or 6950 you may want to upgrade your PSU. If it is a really good quality 450 Watt, you'll be okay with the 6870, though you may be pushing your luck with the 6950. If it isn't a high quality unit, replace it with a better one. Antec, Seasonic, Corsair, Enermax, PC Power and Cooling are all good brands.

Measure the distance between the back of your case and the hard drive cage. Current cards, especially many of the 6870 models are quite long, they may not fit in some smaller cases.