Hi Simon, I recently upgraded my Win7 Dual Xeon to Win10. Not sure my render speed is what it should be. When looking at the resource monitor, no activity is happening on 3 of 4 video cards.
I'm sorry but I do not know. I don't know how well the Win10 GPU monitor tracks true performance. You may want to use a 3rd party GPU monitor. I don't have one myself. You may want to query one of the other forums. The problem won't be Carrara specific.