buy Zotac 750a SLi. i just bought it last week and its aamazing.
Both ur cards will run in SLi each of them at 16x. its bad at OC. 3.6Ghz is unstable on my Phenom II X4 black edition and there is no multiplier and proc voltage options in BIOS. i love the 6 SATA and SLi thing
Why you want a SLI board.. Frankly speaking nvidia didn't have solid turf in Mb market seagment section.. Rio sir had been using them and were never satisfied though it was 680i SLI..
If you want OC the Phenom/Phenom II you better off with AMD 790GX which compliments the dragon platforms and gells really well with Phenom II OC capabilities.. The AMD CnQ, Advance Clock Collaboration and all the components working in sync makes things very easier..
For 5k you can get a BIOSTAR T790GX .. Don't know the exact model but its pretty decent ..
P,s : That 6000+ chip has very little headroom for OC.. So if you want to stick with it any decent baord will do irrespective of nvidia and amd.. You won't be able to push it beyond 3.4