Why does my GPU always run with full clock speeds?
Question:For PCs with 2 or more monitors in Multi-display Mode: Why does my GPU run at full clock speeds?
Answer:
This is a hardware limitation and not a software bug. Even when no 3D programs are running, the driver will operate the GPU at a high performance level in order to efficiently drive multiple displays. In the case of SLI or multi-GPU PCs, the second GPU will always operate with full clock speeds, again in order to efficiently drive multiple displays. Today, all hardware from all GPU vendors have this limitation.
info taken from:
>>> Nvidia F.A.Q. <<<