I think the 5055 will handle the MX7 just fine. Power or weight wise.
The 5055 is a heavy tractor for the ~50hp class. ITs the SAME basic tractor as the 5065e and 5075e. Same rear lift capacities, same machine weight, same engine. Just different power levels.
The MX7 is only a ~1300# cutter. Your tractor is 5500#. IT should run that thing ALL DAY with no need for front weights. (driving up a steep hill with the cutter in the air may not be wise).
My MX5100 is only a 3800# machine, and I carry around a 1600# 8' twin spindle cutter with no front weights. Its light in the front, and I cannot load forward on my trailer, but 90% of the time, the cutter is on the ground and the tailwheels are carrying half the load anyway.
So basically what Im saying, you can handle the MX7 just fine if you so choose. No worrys at all. But perhaps a better fit would be a 8' twin spindle cutter. And heck, if I had a tractor of that size and weight, And no plans to transport on a trailer, I'd even be looking for a 10' cutter