P67 vs X58 + GTX 580 SLI

I've been looking for head-to-head comparisons of P67 vs X58 GTX 580's in SLI within the same post, but so far I only came across the following two posts. I cannot imagine there's such a difference, so either I'm seeing things or there's something apparent with x8/x8 vs x16/x16 in high-end SLI testing 3DMark Vantage Performance setting. I was expecting maybe 10-15% difference and not out of the ball park.

Ideally, you want the same exact enviornment. Clearly, on a single GPU my pick is the P67, but SLI/CF on high-end GPUs my feeling have been leaning towards the X58 until I know there's no difference. I've seen saturation head-to-head with GTX 470's and resolutions at or above 2560 X 1600 showing the X58 ahead.

Interesting saturaturation charts. P67 28,800 vs X58 46,656 or are my eye's all blurry?!

P67 + GTX 580 SLI ; ref http://lanoc.org/review/hardware/motherboards/4642-fatal1ty-p67-profess1onal-series

X58 + GTX 580 SLI ; http://www.tweaktown.com/reviews/3777/msi_geforce_gtx_580_1536_mb_video_cards_in_sli/index3.html

This is a Draft of my tentative recommendations:
I haven't forgotten about them, but they need to update the drivers. Currently, you'll get BSODs with ASUS Maximus IV Extreme in SLI/CF.

M4E 1155 - single @x16, dual @x8, triple @x8
R3E 1366 - single @x16; dual @x16/x16; triple @x16/x8/x8 and quad @x8/x8/x8/x8