you should be flying with two 670s! I have two 570s and I play in 1080 with everything maxed 2xSSAA but no TessFX. And it's smooth. With two 670s you should be able to actually max everything. Especially if you overclock them a bit.. which you really should.
Also I see you mentionned SLI.. currently the game is not well optimized for SLI, but if you use Nvidia Inspector and assign Tombraider.exe to the Hitman Absolution profile you'll get much better SLI performance.
I'm running an older Phenom II quad core and a Radeon HD 6770, 8gb DDR2 @ 1333mhz and the game's running great for me in 1080p with almost everything set at high-to-ultra settings but with AA and TessFX turned off(not really needed anyways)... looks beautiful