Two things. First, set maxfpsbk to 10 for everyone, then, set maxfps to 45 (this is mostly just a test).

Ok, now try again, still have issues?

If yes, when you're having issues, watch your hard drive light, is it flashing like mad or solid on?

If yes, your symlinking isn't working right (or isn't set up at all), or your hard drive can't handle the traffic.

If no, set your maxfps to 30 now, see if you still have the issue.

Are all of your clones set to the absolute lowest graphic setting? Is your main window using FSAA (anti aliasing? 2x? 4x?) Turn it off.

If none of this fixes the issue, go to each WoW window and set the graphics to the BARE minimum, ALL of them, including the main window.

If you still have the issue, I have no idea. If you don't have the issue any longer, then slowly increase settings on only your main window until you have the issue again to determine what the problem is.

Edit: Also, not sure what your CPU affinity is actually set to, but I have a dual core processor and it actually helped me to set my 4 clones to ALL be on CPU1, and leave ONLY my main on CPU0 - even though the clones stutter like hell I can fly with 5 epic flyers without losing follow ever.