If you are using a Decklink card for monitoring, try the optimized mode in the Video Monitoring section.
It might be also worth switching the video monitoring to 8-bit to see if that helps.
Lastly, I would try just losing the GUI card, and using only the 470 to see if that works better.
Make sure your GPUs are on dedicated x16 slots. Some of the consumer motherboard split the PCI lanes when you use multiple slots. Again, losing the GUI card might help with this too.
What CPU type and motherboard do you have?