Stream Processors:

3870 - 320 @ 775 MHz
4870 - 480 @ 1050 MHz

4870 is 2.03 times as fast here.

TMUs:

3870 - 16 @ 775 MHz
4870 - 32 @ 850 MHz

4870 is 2.19 times as fast here

ROPs

3870 - 16 @ 775 MHz
4870 - 16 @ 850 MHz

4870 is 1.1 times faster here.

It should be a very fast card at a good price, I can't wait.