First of all to get 16x/16x you have to get a Z77 board with a PLX chip on it, and they will run you at least $250+.
Second of all i highly doubt you can run over 2800mhz on any board without a CPU which can do it, most retails will only do up to 2666, and most motherboard makers will only advertise up to that, and say its OC dependent. Then you need to have memory that will do those speeds.
Also memory speed make minor differences, and if you want future proof just look for memory density not speeds. There is a ripjaw-Z kit coming out that supports high memory speeds and is 16GB, like I think it is rated at 2800 if they found enough chips to actually do that, or they would just rate it at 2666 b/c it is hard to find chips to do 2800. I used one of those kits, but it was strictly ES sample kit and it did 3GHz memory and 2800mhz stable with all 4 DIMMs, but it took a lot of CPUs to find one that could do that.
Next the boards with the PLX chip, the top end ones at least aren't released yet. There is the ASUS P8Z77 WS Revo has that chip, and then the G1.Sniper 3 has it too, and i think the asrock z77 extreme 9, and evta Z77 FTW. I think the Maximus 5 Extreme will prob have that chip too, but the Maximus 5 formula hasn't even been released, so god only knows when the extreme will be released.
For 3-way SLI you will need a PLX chip.
The G1.Sniper3 would be my pick, as that should be in retail soon, or the Maximus 5 Extreme whenever that comes out, or an unnamed board whenever that comes out.
BTW running two GPUs at 16x/16x with the PLX will bring you benefits like maybe 2-3% over native 8x/8x, about as much as running your memory at 2800mhz+ opposed to 1600mhz when you talk about practicality of things lol in each case only practical to extreme benchers. IMO just go with a normal Z77 board, aka no PLX. Sabertooth is cool, i like the Z77X-UD5H, but you gotta like the blue to like it.
