Temperatures & Power Consumption
The 70 degree stress temperature of the Radeon HD 2900XT comes at a price. Peace and quiet is something you will never get with that card. In the other hand, the Radeon HD 3870 was a very quiet graphics card though as a result the operating temperature levels were considerably higher.
The 55nm design of the HD 3870 GPU along with the power efficiency offered by GDDR4 memory has paid off. As you can see, the 3870 does have a very low idle power consumption level, using just 17 watts. Under load the 3870 also used less power than the GeForce 8800 GT.