You gor low framerate due to 2 reasons:
1) For better performance you should minimize total count of DrawPrimitive calls per frame. Optimal is about 500~1000
2) Triangle you are drawing is LARGE, so your bottleneck not in geometry engine of GF2 but in FILLRATE - shrinking triangle size will give you better framerate.

You could get about 10~20 million triangles per second on GF2 card in optimal case.