Although this is not exactly what are you asking, you might want to try
Leatrix Latency Fix (if you did not already) to lower your latency. It can produce pretty significant results (around 150 -> 40 for me) just by changing the way Windows are ACKing network packets. No side effects spotted over 2 years of usage.
Also, WoW build-in "latency tolerance" can work quite well if you set it up correctly. It's pretty simple - if you enqueue your abilities in advance, they fire at the very moment GCD gets ready. You can't possibly get better than. The only downside is when the threshold is set too high and you start queueing wrong abilities before you even want to.