BlackMagic Decklink Output Pixel Format 10Bit

If I put my Video Device Output (Decklink) on 10-bits Pixel Format I get a lot of high values for Downloading texture Data from GPU. Around 8 to 9ms (not for each frame, but for a lot of frames). Does anybody know how to get rid of these high times? It works perfectly if I put it on 8 bit, but the 10-bit output looks so much better. Do I have to convert my input first for this?

I am using the latest experimental build: 30790, but also had this in previous versions already too.