If you're cutting 1 inch or smaller pieces, I would reconsider the RC2072. The MX6 weighs 350 - 400# more than the 2072 requiring not just more ballast, but also causing more pitching motion of the tractor over uneven terrain. The faster blade tip speed of the MX6 will give a better cut potentially, but my 2072's cut has been excellent. The heavier and longer your rear attachment, the more it affects ride despite adequate front end ballast, something I've seen with my shorter 3038e and the RC2072.
Your 4120 should have no difficulty powering either hog. I've had no problem whatsoever powering a 6' hog with 5 fewer PTO hp than your tractor, and considerably less operating torque.
Your 4120 should have no difficulty powering either hog. I've had no problem whatsoever powering a 6' hog with 5 fewer PTO hp than your tractor, and considerably less operating torque.