Thanks. Actually, I am going to share 3 cards on an x1!! Yes, I expect a massive performance cut haha, but it should be more than enough bandwidth for mining (if it wasn't clear, that's why I'm doing this).
But I will run some tests out of curiosity. A single 1080 Ti suffered a 20% performance hit on an x1/USB-wired riser (Unigine Heaven 1080p max settings). I expect a 1080 Ti + 1070 + 1070 on an x1 to suffer a much more significant hit each, but it will be fun to see how much.
Thx for the explanations!
I wasn't sure it was for mining but with 3 cards on an x1 it is now quite obvious!
I made a quick search but it looks like USB3 PCIe riser x4 doesn't exist. Probably because USB3 can not support such a bandwith, dunno...