well heres a thing ....!!

dunno if anyones seen this b4 but if youre worried about performance in gaming when mixing x8 and x16 then worry no longer.
The boys over at Hard OCP have done some pretty convicing testing using sli and crossfire at x16 and x8 and there is almost no difference !!!
Ok the board was not an R3E but I bet the results would be similar, maybe Ill put my Phys-x card back in ( tbh I never did see any drop in performance with it in there, but when I noticed gpu 2 in lane 3 was at x8 I took it out !)

http://www.hardocp.com/article/2010/...6x16_vs_x8x8/1

just put them where they look best :-)