I run a 62" Flail mower on my
BX2200 and it's only 4 more HP than that
BX1880. Lifts it and turns it just fine.
I can mow about 2' field grass/weeds with it, and it only slightly bogs down. It actually sounds like it's working -- which is a good thing.
However, I take my time and mow at a reasonable speed for a good cut.
If I'm using the flail mower, depending on what I'm mowing and the terrain (or hidden obstacles like rocks or stumps), 2-4 MPH.
With the MMM, can vary from 2-5 MPH.
Not much difference and eventually the job gets done.
Going too fast mowing doesn't do a great job, even with those zippy zero turns.
The slower you go, there's more time for lift applied to the grass allowing it all to get cut evenly versus getting matted down or simply missed all together.
When I was younger, I used to do lawn care and one of the tricks to gain extra cash was to go as fast as we could, not only to get to the next job but -- the customer would need their lawn mowed almost twice as much.