CPU for rendering, GPU for the viewport. unless you hook up some 3rd party GPU renderer, I suppose.
i take it 6.1 is the trashcan model? CPU wise it should be good to go if you get a decent configuration - 3.x ghz, D500 or better. viewport should suffice for day to day work unless you are playing around with shaders and realtime preview alot. if you want to work in front of it rather than just render then it’s better to get one with few CPU cores with high clockspeed rather than some of the configurations out there with 12+ cores but running at 2.x ghz.
storage would be my concern though - a single SSD inside that thing and you can’t replace it (easily) yourself as far as i know.
speedup coming from an MBP should be quite noticeable. obviously don’t compare with a recent PC. but you know that already.