If anyone cares, I've figured out when the X series upclocks to 3D clocks. It seems to take a fullscreen 3D game.

HL2 EP1 triggered the 650/1000 of the X1950XTX card. This is with Win7 and Catalyst 10.2 Legacy. See the change on the GPU Core / GPU memory graphs of GPU-Z below.

Forgot to say, that I fixed this problem about a week ago. I installed Catalyst 10.2 through Device Manager, and all my GL games work flawlessly without any preformance hitches or flicker.