The good news is that there is some discussion in sibling threads that seem to indicate the 8x slot will lose you maybe a single frame per second. You can check

The good news is that there is some discussion in sibling threads that seem to indicate the 8x slot will lose you maybe a single frame per second. You can check what your card is running at using GPU-Z, make sure to run something intensive as the card will enter a slower state to save power when it isn't being used.