update: I just figured out as my mac pro has usb2 (usualy I shoot to the macbook ) and a usb3 pci card. So I tested both connections with my 5dsr.
Result, both need about 2 seconds to have the image appear in c1. (btw: LR is slower to my experience, but I did not test that this time)
So the USB connection indeed does not seem to be a limiting factor for tethering.