Firstly , let me say you do not need two 680's at the present time. The reason the poster would more then likely need more then one card is primarily do to the fact that he is using a 3D vision setup. I used Batman Arkham city as a example because its DX11 game that is extremely taxing on computers now and when you add Physx on high and tesselation and AA+AF you end up with a crazy amount of resource draw. What I would suggest for you is this if you want.
Grab a gtx670 and if you need for physx use your 570 as a physx card. You do not need to use a sli bridge just plug it in like normal and go into nvidia control panel and set your physx settings to that card.
Interesting. The regular Twin Frozr MSI 570GTX is $279. Very intriguing to get that then, SLI it, wait for spring and if anything great comes out....sell them and get new PCIe 3.0 card(s).
The fact that the keplers are 256bit makes me wonder.
Hmm what to do???? I see 670 and 570GTX for Physx/ Bigshooter; would it be a waist to do this? Is there a way to monitor the framerates and see if my system takes a hit? GPU-z?