I use Photoshop CC and work in Adobe Camera Raw a lot. I upgraded my computer a couple months ago:
- My previous system: i7-4771 (3.5Ghz), 16gb DDR3 RAM, GTX750Ti, older HDD
- My new system: i7-6700K, MSI Gaming Carbon motherboard, 32GB DDR4 Ram, GTX 1060 (6GB), Samsung Evo 850 SSD
I did not experience a big jump in performance. More RAM definitely helps when I edit more files in ACR. SSD helps loading and saving stuff, but still no dramatic difference (at least not in Photoshop/ACR). Also, editing steps such as geometric corrections, local adjustments, etc. did not become much faster in ACR.
I don't think Photoshop/ACR can properly utilize a powerful system so we're basically facing diminished returns above a certain level of equipment.
The general consensus is that more RAM and a higher clockspeed processor (as opposed to 6 or 8 cores but at a slower speed) helps most in Photoshop/Lightroom. Most tasks cannot utilize more than 4 cores.
Funny that my current system would be great for gaming but I never ever do any games. 
p.s. One thing I did notice was that when I switched from a 1080p monitor to a 1440p one, it considerably slowed down Photoshop/ACR (using the same computer). I believe doing it in 4k slows it down even more.