I ran a 50 in rear mount on mine for a year with no problems. Went to a front mount due to the literal pain in the neck of a rear mount. It's all relative with snowblowers. You could run a 72" if you crept along very slowly.
it seems to fit in the HP range for the 50", 15-30HP. We ran a 60" on a 755 with no problems. I currently have a 54" frontier on my 2320 and I don't see it being a problem.