Not true. They will run at their default overboost clocks. Just make sure the power targets are the same on each card, otherwise you will be in the hole I was in fightimg with drivers. So check in MSI sfterburner what your max power target is on each card. I.E 145% If they are the same, then you shouldn't have any problems.
As long as they have the sameish clocks and same memory size, it is fine. When mixing brands I always used to just take the lazy way and flash both with the same bios.
Oh right! For an inexplicable reason I read 580s. Hey TrueGamer, when you get rid of your 670s, want to send one over my way? I kinda want SLI.
I tried that on the SC card, and it made no differences... Still had problems. Could be down to having less Capacitors/Phases perhaps. I don't plan on upgrading for a yr or two on the GPU's. Unless the GTX 780's leaves the Titan in the dust.
It's all good, I'm just looking for a rather cheap GTX670 Cheesecake as I have one already. Who knows, Tri SLI?