Correct. Only when running a 3D app, and only when SLI is enabled.
I TRIED to stress them simultaneously, but can't seem to figure out how to do it. No matter what screen I move a 3D window to it always uses the primary card for rendering.
Try this for a quick stress:
1. disable SLI in NVCP and select one of the 2 cards to render Physx
2. run Mafia II Demo benchmark with Physx set to High
The main card will be stressed well and the Dedicated Physx card will be stressed to 60-80%.
3. repeat again after switching roles of the 2 cards