Ok well let's start with how do you know it's giving you more performance if you never showed it running on 1 gpu? then you claim because you pressed f4 twice now it works magically and you get 140fps from 80 but you're staring at the sky....... look at 00:15 before you did that and 04:30 after you claim it's working but this time your looking in the same general area and your fps is no different than before. Then you show us that your not running at a native resolution but at 50% of course you getting good fps if you cut your resolution in half. But running the game below your monitors native resolution makes it look even worse than on a native 1440p monitor because of interpolation.
Never the less i humored you, double checking exclusive fullscreen is enabled, using your newest profile and pressing f4 twice and boom it worked!!! ... lol just kidding it did nothing. I suggest you try running the game on a single gpu looking at the same spot, same time of day and same settings. I suspect your in the same boat as me, i've yet to see any real evidence that sli works in 7dtd (and by work i don't just mean it's enabled and the game is running, i mean give more performance than a single gpu)