any other similar option that has SLi and not nvidia?
The only non-Nvidia board that support sli is the extreme high end dual cpu Skulltrial, supporting both cf ans sli, including quad cf/sli. But it'll run you $600.
High end Intel boards for the i7 will support sli, but it won't work with existing Kentsfield/Yorkfield quads.
780i is good enough to hit 1600mhz fsb, which translates to 3.6ghz for q6600(9x multiplier). It won't be enough for newer Yorkfield 45nm quads though, since they use lower multipliers. Q8200, for example, use 7x, which is only 2.8ghz at the same 1600mhz fsb.