Are your slaves all running at lower settings? You don't mention framecaps on the slaves. There's a good page over on ISBoxer.com about framerates, most of which is still relevant. The only differences {offhand} are - you'd need to use ingame commands or the ingame slider directly to set framecaps

/console maxfps 60
/console maxfpsbk 10

The first macro sets a maximum FPS of 60 while the game is in the foreground. The second sets the maximum FPS while the game is in the background {slave instances} to 10 FPS.

The second difference is no "CPU Strategy Wizard" in HotKeyNet, but you can still do a lot of the same things with ingame macros. Use the SetAffinity command for Hyperthreading. For a lot of other bits, you can look over some of the old "FPS Saver" macros. I can't speak to the cvars being uptodate or even valid for WoD, but it's someplace to start.

Keep in mind, new expansions mean new graphics. WoD gave us new character models and prettier ground clutter, both of which can be a performance hit. If it's been a while since you've played {which your post history indicates}, MoP also increased the actual distance of View Distance settings and added some stuff like SSAO, different refraction {IIRC}, DX9 vs DX11 that impacted a lot of people. You should revisit all your graphics settings if you're playing an old, updated version, though you'll probably save yourself some headache simply using a fresh install.


Outside of that, I'd make sure you've limited the addons on the slaves to reduce the load - no need to have Auctioneer loaded 5 times or whatever. You can even use something like this in the FPS Saver/swap macro to enable and disable addon sets as needed.