I would suggest to keep a "balanced load" on the gfx Card.
Recently had it on the Weekend with a Macpro and ATI X1900 with only one THTG and a normal Monitor on one Output I had a kind of stripe ghosting on my outs.
of course it had to be the Projection guys, as it looked like a power issue, but everything we tried did not solve the Problem.

The I added a second THTG to the second out of the Mac and the ghosting was away.

This belongs to X1900, can't say anything about other GPUs but with that I would recommend not to misslead the GPU.

Best

Rolf