I was waiting for a new mac pro update, but no USB3//thunderbolt//sata3, makes it hard to invest in. So I'm going to the apple store tomorrow with my external, and headphones, and I'm going to load up a normal session, and put as many plugs as I want, and then Open up another program to simulate adding melodyne, then hitting play with activity monitor open and See how it holds up.
If it holds up then I'll grab it, and a R6 and a thunderbolt display.
If not back to Mac pro