I'll start off with my specs:
CPU: AMD Athlon II X4 651 @ 3.2 Ghz
GFX: GTX 760 twinfrozr 2GB GDDR5 stock (because OCing it seems to completely ruin any chances of the game running for more than 20 seconds)
6 Gb ram (generic) @ 1,666 Mhz
Driver version 352.86
Win 8.1 x64

I've kind of run into a wall here, and can't find anything anywhere about this garbage performance regardless of what settings I use.
I get a high of 14-20 fps on all low settings with everything turned off at 720p with framerate capped at 30/60 as well as unlimited.
If I set the resolution to 1080p I get a max of 14-16 fps with all low settings.
But if I set it to 720p and put everything on high (minus foliage distance which I set to medium) with most performance affecting options in postprocessing on, and yet I still manage 14-20 and if I change the resolution to 1080p I'll get the same as before.
Hairworks is completely off in both tests.
I've tried using the settings in the Nvidia control panel and geforce experience recommended but absolutely nothing matters.
I've even gone so far as to uninstall and reinstall the drivers and even roll back to earlier ones to no avail.

I had a short stint where I could run the game buttery smooth at 900p with all high settings but the game crashed and stopped working well altogether. I have uninstalled and reinstalled multiple times with all the patches.

It's seriously driving me Nucking Futs.

Has anyone else encountered this or have anything at all that could help?

I suspect there is something strange going on on your system.

I also had an GTX760 (upgraded to an GTX970 a few day's ago), and I can tell you I got at least 30fps (and most times higher) on 1080p and most settings between medium and high. I must say I have an somewhat higher spec. processor (I5-3570), but I have seen in many benchmarks that the processor does not have the same impact on the frame rate as the video card has.

It sounds strange, but do you have the latest chip set (motherboard) drivers installed? It should not make much difference, but you never know. Also - make sure you have defragmented your hard disk. I know - it's not much, but that are the only things that comes to mind now..

Changing mine from windowed full screen to full screen and disabled motion blur fixed the problems I was having. I went from 20fps to 60fps (with sli gtx980's)

Yeah I've installed the latest mobo drivers and have defragged my hard drive since installing the game.

I think I'm just gonna have to wait for a patch or get a new card/CPU.

I have tried switching from windowed to borderless to fullscreen and everything, nothing has helped.

Best guess is you have some software running in the background that is conflicting or using up cpu and/or gpu cycles.
You could try killing all unnecessary processes and see what happens. Personally if this was happening to me I would probably reinstall windows.

There must have serious problems because your specs are a looooot better than mine and I get only a couple of fps less. This is strange, because I have better specs than others and still do worse than them. Don't know what's going on.

I found out what the problem was ladies and gents.

What I had downloaded was the pre-load installation files, not the up-to-date ones.
I had been re-installing the game with those files and perhaps they were corrupt or something because I re-downloaded the newer setup files. Thanks to for Fibre Optic internet it was done in...I think 4-5 hours.
Now I get a fluid and uninterrupted 30 fps with everything on ultra (minus foliage distance and the hair garbage) with all the post process options on. The game still doesn't like when I try to OC my card though...oddly enough.

Chalk this one up to my inability to think of the simple things. lol
Thanks anyways everyone.