FPS stutter on combat only, Warmane relm only, multiple PC's WTOLK servers only
About a week or so I started noticing sever FPS stutter on all 3 of my PC's when using Icecrown, or Frostomourn Warmane servers . 100+ FPS in any major city/dalaran, etc, but combat with even a single mob will reduce FPS to a slide show - 2 to 3 FPS until combat is over, then back to 100+ fps. This happens on my Desktop gaming rig, my laptop and my wife's desktop gaming rig, so I'm fairly sure this isn't HW/SW on my end. Our internet connection is +400 MBPS and our latency is around 150 ms.
Here's the kicker: I can set my relmlist to other private WOW servers and I do not experience the same problem. This started a week or two ago. I have no added any new addons (using same set for the last 5+ years). I have removed the cache/WTF folders...all the tricks I could find to no good result (even tried the /console SET ProcessAffinityMask trick, but that did not help). I'm using the same wow files for the Warmane servers as I am for other private servers with no issue.
Last point of note - I can run MoP with zero issues.
I've been dealing with this for over a week - no new addons where added. I removed all the addons from the interface directory (copied them to a temp dir) - no change, still stuttery as hell. Out of desperation, I downloaded a new torrent of the WOW client from waremane and that resolved the issues. No more stuttering. I believe that the wow.exe and related files may have become fragmented, or corrupted over time (years). I do not believe it was addon related, because I took the same addons that I previously used and moved them from my temp directory into the new install of WOTLK. No issues.
so...TLDR;
if you are having severe stuttering issues out of nowhere, try downloading a new copy of the torrent and migrating to it.