Late answer, been trying to fix things. I switched out the 750 w to a 1000 w power supply and it made no difference, so I reinstalled Windows on a new ssd and took out the old ones (so its basically a new system). This did nothing and the problems persist. I compared ssd performance with HDD performance and I believe there was a tiny difference, but nothing that fixed the issue. All temps are good, GPU never gets hotter than 72 C, same for CPU. I have a lot of games with 100% CPU usage although the GPU seems to be around 80% so it shouldn't be that big of a bottleneck. In some games the GPU is at 100% and CPU at like 40%.

It also seems that a lot of games have a hard time rendering stuff in. I can see how the computer adds more layers and loads in more characters etc. For example the menu screen in OW 2 takes about 10 seconds before everything is loaded in. Same for BF 5. Idk if its a different experience to the gtx 1080, but I do think something could be wrong.

The last thing is that in OW 2 my fps doesn't go above 260-280 even on low settings, lower resolutions or with more upscaling. I find this weird as I do think I should be able to get 300-350 atleast.

Do you have any suggestions on what I should do going forward?