I had this experience with IDL in P2010, but with 2012+the SRs the issue with slow hair rendering with IDL has been much improved. Do as suggested and only enable raytracing and light emitter for the final render.

I wouldn't even think about not using IDL - it (and EZSkin) are the best things to come along since sliced bread. And combining bed and bread motif - for Dave-So:)