Every MoBo I've seen, mine included, walks them down to 8x when doing SLI. And I am well aware that there is no noticeable difference at all. I'm only asking out of sheer curiosity if there are any MoBo's that do SLI with both at 3.0 and 16x.
https://www.asus.com/uk/Motherboards/Z87WS/ can do it if you only use 2 cards I believe. --- Fan of metal? Don't mind covers? Check out my youtube and give me some feedback http://www.youtube.com/sircaballero
On the Z87 platform, you'd need to find a board with a PLX chip. There are a few high-end Z87 boards thus equipped. Native support for x16/x16 is more commonplace on the X79 platform since it has more PCI Express lanes. --- -What is best in life? -To crush your enemies, see them driven before you, and to hear the lamentation of the women.