He's right the CPU would be the bottleneck but I have a slightly weaker CPU, same GPU, and rarely drop below 60FPS with all graphics maxed at 2560x1440. When I do drop it's the CPU but not in "most situations" just when lots of stuff is going on then maybe 40FPS worst case?
Open Task Manager then:
1) confirm you can see all twelve CPU graphs (if one right-click to enable all logical)
2) confirm the approximate CPU frequency under load in WOW and the Intel CPU diagnostic
There may be a better method but I'd probably just run WOW in Windowed mode to observe the CPU frequency. Or use an OSD tool if you know how to use that to show the CPU frequency.
*the only OTHER thing I can think of is that your GPU is being throttled for some reason. However it's going to drop frequency if the CPU is the bottleneck so it's hard to tell.... you basically need to see if it's frequency and GPU usage are fine in OTHER games and benchmarks.
Here is my Unigine Valley results. If you want to compare run the EXACT same settings.
Unigine Valley
-DX11, Ultra, x8AA, full screen, 2560x1440
GTX1080
- 68.4FPS avg
- 2863
- 32.7fps low
- 140.3fps high
Your results should be close to that. WOW is more CPU intensive but this should verify the graphics part.
Other: I'd also run the Intel CPU diagnostic
https://downloadcenter.intel.com/download/19792/Intel-Processor-Diagnostic-Tool
It used to kill my overclock until I rebooted but I don't think recent versions do that.
Other: not sure of your overclock but my i7-3770K is at 4.4GHz.. the i7-5820K max Turbo is only 3.6GHz so it's probably running roughly 3.5GHz in WOW at default settings... sounds a lot lower but your IPC should be slightly higher so gaming potential is probably about 10% difference comparing my CPU at 4.4GHz and yours at 3.5GHz.
(hitting 4.5GHz sustained vs 3.5GHz would be almost 30% overclock to be clear)
You SHOULD overclock that CPU if you have not and it should probably reach at least 4.4GHz assuming good silicon, motherboard supports OC and a half decent air cooler like Noctua NH-D15s or similar.
other 2: one potential issue that's unlikely is really low DDR3/4 memory bandwidth. Like a single stick may or may not cause a big drop in gaming performance. Hard to say.