This can probably be solo'd now, but easily duoable. With the changes in Underfoot to the RS pet AA, this should now be had by all magicians. This will save about 60m per cast on Rumbling Servant (assuming not casting on GoM proc of course.)
Necros would also like this, as most i know 2ndary forte in conjuration or some even primary specialize in conjuration. The CoA necro hat has 12% to conjuration since a lot of our high end dots are conjuration. But i still recommend alteration as the primary specialize since our taps, taps over time, and highest dmg fire dots are alteration.