Rob Walsh

Try adding some voltage to the GPU core to see if that improves stability. Re-pasting a GPU isn't hard, just more small screws, if you go slow it's fine, but let's not jump to hard solutions before the culprit is known.

Word on the streets is Vega 56/64 may be getting AMDs version of ray tracing.

That being said, it may be worth a wait to find out more on NAVi. Just because AMD doesn't always beat out the competitor with their performance doesn't mean they don't beat out their previous models. 

Take that with a grain of salt though, the R9 series I've found was a lot more reliable than the RX series. ( and the RX series didn't out perform the R9 on most games either ).

I personally love team red, but I was sick of the waiting for NAVi and went for a 2080. ( now they're $250+ cheaper than when I bought mine). 
Price for performance is very cheap and depending on what system you're running the VEGA 56/64 pairs well with everything newer than an 8350.

All that useless info aside, I'd go for a 2070 with your build or wait for NAVi. I know price can be negotiable, but with that CPU you're going to be able to use any GPU you want. without bottleneck ( higher the resolution as well, the better they'll pair ). Saving a couple more weeks while you wait for navi has got to be better than "settling" with a lesser brand of GPU because you need 'something'. thats my opinion however and if you plan on running 1080p at 144hz you better look at a 1070 too. 

The motherboard is a h87-d3h Gigabyte and the CPU cooler is the Corsair H60. I've been using this computer for 6 working on 7 years now. Would it still be okay to overclock the CPU?

Did you go ahead and check thermals? It's possible it could be thermal throttling. But even at 40% usage you should be getting higher than 65 fps on wow. it was made over a decade ago. when was the last time you dusted the machine? If the GPU is doing well in the Benchmark ( whichever one you're using ) then I think we can rule out bad silicon. Keep in mind the 980ti was released in 2015 and is now 4 years old. Old hardware can go bad. As does everything! have you checked your drivers lately? That is the sort of thing that you wouldn't find on a 980ti but Even on my old R9 I was getting driver updates last year. 

I understand friend, here's the thing. you can get a b350 bundle with 1600 and still be able to afford you 1060 6gb. You r e a l l y shouldn't buy a 580, you're going to hate it and its around the same price for a much better card. Please don't make that mistake, Perhaps stick with the quad core for now. buy the 8gb stick of ram and that saves you 50 dollars., if you think about it you can afford the 1600 build if you get only an 8gb stick
 

@Rob WalshFirst of all thank you so much for your detailed and helpful answer, I know exactly what you mean but the economy is not that great at the moment sadly so I actually can't go for that good of a PC, that's why I wanted to settle for the previous suggestions even though I would rather want to go all in.. 

the BIGGEST thing is to make sure you get a motherboard that is *2000 SERIES CPU READY* that way when you get more money next year you can buy the next gen cpu and bolt it in (after a bios update ofc). Or maybe even upgrade to a 2600/2600x cpu this year lol. the difference between the 1600/2600 and 1600x/2600x is the x doesn't have to try as hard to overclock because they're built with handpicked parts - silicon, die etc. The only real difference is sometimes you get a 1600/2600 that is just as good as the 1600x/2600x and you can overclock it almost just as high with watercooling ( or in some cases perhaps just as high or more lol ) its lottery when you buy the non x versions. Sometimes its great sometimes its bad. The way silicon has been going lately you could get one that just sucks in comparison. I like the premium of having the x but im kind of weird like that. Almost everyone got the 1600 because they wanted to save 30-50 dollars. I recommend spending a bit more for cpu because if you get the quad core its going to be about half of what you could have and you'd want to upgrade pretty much instantly. 

            Quad core gaming used to be good enough, its not anymore. You cannot play dayz on a quad core from amd. Not arma or any of those, they don't have enough L1 L2 Or L3 cache, and you'd need the fastest SSD around ( nvme ssd ) with some kick ass not cheap ram. The 6 core 1600/2600/x all are basically the same as the 8 core with less cores and threads respectively. So you're getting that performance that I like to call " worth the extra dollars " everyone will try to make a build for you thats around your budget. But you're going to work your A** off for this any way, because you're an enthusiast. What's another 200 dollars for twice the performance ? That's exactly what I thought when upgrading my pc. I just worked 15 hours yesterday to try and save up for a 1080 lol. 
      Anyway my point is you should get the 1600 if you're going to upgrade later, or buy the x470/2600(x) combo that will be on newegg or amazon soon. (either or man its up to you and how hard you wanna work and how bad you want a good pc, so x or not you have the info to make a good decision based on facts) I would do the latter, I would get the better stuff and save up for other things like car parts or games AFTER you know you won't have to upgrade for at least two years. BTW you can always upgrade later, so if you want to save money and you're not going to be playing games that require more than 8GB of RAM just buy one stick of 3200mhz or faster ram (1x8gb @3200) and then upgrade to another stick later on in life ( of the same exact type and brand of ram i.e; 1x8gb stick of 3200mhz rated ram.) 

            I can link you to stuff on newegg ( that's what I use mostly ) if you like. 

spend a little more cheese and get a 6gb 1060 and a 1600x

!! Precisely my point lol its a STEAL for anyone who wants to game for cheapsies 

Looking at it again, you're probably right about the R9 390. I was going off Fire Strike graphics scores, but the cards seem to manifest their performance different game-to-game.
 
As for "a tiny bit more", you actually have a point, The GTX 1060 6GB Dual from ASUS is $289.99 right now, and that's a better card than either the R9 390 or the RX 570 4GB. 

my friend had a strix 580 and it didn't come close at 1080p 144hz... so I don't know what you mean. What's *dumb* is paying for a 570 when you could pay the same, less or perhaps a tiny bit more for a much much better card. the 1060 6gb, I just bought one for my girlfriend and it gets higher scores on userbenchmark than my 390.. she has an fx8350 build with non oc slow ddr3. 


edit: i was also recommending a different card than mine, I know there are better less money alternatives.