You can't expect much more than you got with GPU accelerated PhysX games until further in the future. For now, there isn't many GPU's which can support it in any form, and the ones that do, still are very limited in performance. The tech is in its infancy for gaming.
I'm just saying the tech is based on smoothing/blurring of lines to make them appear less jagged. MSAA and SSAA variants get help from the game engine to achieve a better result and post processing versions don't, which result in less clean solutions, and look blurrier. My point is still that...
When you reduce the image, and combine pixels into one, and pick a color that is an average of those multiple pixels, that is blurring. Even SSAA results in a slightly blurred image. It's just as bad as post process AA. Or rather, the blurring of pixels with SSAA and MSAA is better than...
How much blur that occurs is dependent on what form is used, but the whole tech is based on blurring the lines to smooth the image out. AA is blur in all forms.
He might be thinking about how PhysX could be performed on a 2nd card, even if they weren't the same. At this point, I've not heard of this being a possibility, and let's just be honest, it's not going to be worth the money, even if it did.
It's only worth considering if your performance needs are beyond what a single GPU can do. Don't ever consider it with mid ranged or lower cards. It's just not worth it. The way support has been lately, I question whether you should ever consider it, but definitely do not do it with mid...
It could be an issue with the Nvidia software. Only some Freesync monitors are not available for G-sync, and they might not have the ability to detect and allow for monitors, in a reliable manner yet. I'd post a bug report to Nvidia.
Many games simply can't get to 144 FPS no matter what GPU you have, usually because they aren't designed for it, and the CPU becomes the bottleneck. Chasing 144 FPS in all games is a fools errand. Be happy and wait for a more significant upgrade.
Did you mention the resolution of your display, maybe the refresh rate as well? At a high resolution, the 1070ti would not be bottlenecked, but at a low resolution, it would.
There are a lot of ways a game can still be bottlenecked. Borderlands 2 may be using a lot of PhysX, which those features may be bottlenecking you. Your CPU can bottleneck you at 30%, as it only takes 1 core to go near 100% and slow down the rest of the system. Not all games will use all the...
Just because it's a 500w unit, doesn't mean it's not the PSU. They do go bad, they can even be defective out of the box. I'm not saying that's what it is, but it could be.
You might also look for a copy of the original BIOS on it. It's possible someone messed with it before you got it.