Mother board - Best SLI gaming performer.

I think theres a Giga-Byte, but that has like 4 PCIx16slots, and wouldn't want that. There are no performance advantages of going to full x16 bandwith. In fact in most benchmarks, the dual x8 won (by VERY little, woudln't even be noticable).
So, right now, the best dual x8 mobo would probably be the DFI LANPARTY nF4 SLI-DR or the Asus A8N-SLI Premium.

there's no advantage to it. x8 is just as fast as x16 with today's cards. Which means next year's cards won't show a noticeable difference either.

How do you know that next years cards won't show a noticeable difference. Maby next years cards will actually use all that bandwith.

Because that's the way things work! It takes several years of advances to push a bus.

AGP4x was introduced in the TNT2 days. We sat through the GeForce, GeForce2, the GeForce3 was the first one to show a measurable difference between 2x and 4x, and the GeForce4 Ti4200 was notable for showing a noticeable difference (as in, a few frames per second) between 2x and 4x. Then there's AGP8x, today's fastest AGP cards show pathetically small differences between 4x and 8x. 8x has been on the market for how long?

So far advancement has been at a predictable rate, my comment makes a very safe assumption that it will remain at a predictable rate.