Just my two cents to repeat:
1) RAID performance, again, to my understanding is a CPU issue. The fastest cores, such as an i5-7600K or i7-7700K.
2) For most things, in general, I like building around the R5-1600 (6C/12T CPU) RYZEN but it won't be the best choice for WOW in particular.
3) I can't find really good BENCHMARKS that show how CPU's compare in large RAID's so much of it's anecdotal but the evidence is pretty solid and common for MMO's to be CPU limited with larger maps especially (more data to be processed client side).
4) If you don't want to overclock, that's cool as the i7-7700 is pretty high, but frankly I'd try to get to a motherboard that supports Intel's OPTANE memory. It's pretty awesome. Then LATER ON invest in a stick of 32GB when it's $50 or so.
5) I started a build but it's really FRUSTRATING trying to balance everything to stay in the budget because I like to put in a more expensive MOTHERBOARD than most people so I usually end up with a cheaper graphics card. Also wanted an SSD but trying to stay on budget AND fit in an i7-7700K (which I felt the best choice for WOW and having some future proof to thread count) might be ideal.
There's no perfect solution frankly.
Also, I don't play WOW anymore. Exactly how LOW are the dips? If you can mostly maintain 60FPS with occasional above 40FPS dips on a RYZEN R5-1600 then maybe consider that as an all around good CPU with future proofing in the threads for future games, multi-threaded apps, multi-tasking etc.
6) If you can't maintain a mostly solid 60FPS, VSYNC ON experience then I would recommend forcing on ADAPTIVE VSYNC which auto toggles VSYNC ON and OFF.
The purpose of this is so when you drop below 60FPS you don't add STUTTERING which is what you get if your FPS can't match the Hz rate (60FPS at 60Hz). With VSYNC OFF you then get SCREEN TEARING but that's preferable IMO to stuttering/lag.
and me to mine 
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