2x[r9 280x manual OCed] crossfire, pcie comparison

[ZhyrikaN]

i am planning to OC powercolor 280x's to highest possible clock speeds and crossfire them. in a site, there were fps results of 2x7970 at stock clock speeds on pcie 2.0 x8 vs pcie 2.0 x16 pcie 2.0 x4 vs 3.0 x4 vs 3.0 x8 vs 3.0 x16 and even at 1.0 x16. the results were almost the same, maybe %1-2 difference.
so my question is , am i still going to get nearly max performance (compared to 3.0 x16, max %5 loss) with highly OCed 280x crossfire in pcie 2.0 x16/x16 slots? and what about 2.0 x16/x8 ,, x16/x4 and x8x8?
note: at 1080p.

 

[mouse24]

Theres no noticeable loss at all with almost any current gen cards in xfire/SLi on 2.0 x8 and above. (2.0 x8 is the same as 3.0 x4 and 1.0 x16)

 

[ZhyrikaN]

Theres no noticeable loss at all with almost any current gen cards in xfire/SLi on 2.0 x8 and above. (2.0 x8 is the same as 3.0 x4 and 1.0 x16)

even with r9-290x xfire or gtx 780-ti sli?are you sure? because im gonna get cheaper mobo so i dont want to regret doing that. and just tu be sure can you prove it with a link or something, on OCed 280x or 290x or 780ti?