Zader vs Rancor

Gear and speed is huge. The more often you can hit the rancor, the more TM you can take away. And the more damage you do per hit, the fewer hits are needed to kill it and thus fewer chances for the RNG to screw you over. Potency isn't an issue if you have all Empire/Sith (unless you want to inflict Speed Down) since their TMR can't be resisted if it procs. Even if you have non-Sith/Empire, you don't need potency if TFP is modded for crit chance.

I run Zader, Sid, TFP, Rex and QGJ and have been doing pretty well so far. It easily handles the whole raid on manual. I've only run it twice on auto: the first time finished it and the second time died early in P4.