For the most part an 8800GT and a 9800GT are identical. The only real change is that the 9800GT uses their newer 45nm die process, while the 8800GT uses I believe a 65nm die process. Thus the 9800GT will tend to run a little faster, take less power, and generate less heat than the 8800GT.

When running 5 pcs, I prefer lower power/heat...