I'm like Don in that the flail mower is maybe my favorite implement. I seldom get into trees much bigger than saplings but I have 4 small meadows which I leave grow Spring through Summer for ground nesting birds etc. then cut it down in early Fall so the weeds and brush gets pretty tall and thick in some places. The 25hp L2501 I have is about the same as a lot of your machines and it has no problem with the 60" Woodmax. https://www.woodmaxx.com/FM_62_Flail_Mower_p/fm-62.htm For my kind of use Woodmax recommended Y cutters which supposedly give a little better cut, in addition they are reversible, so that's what I went with.
Anyway I'm very pleased with the quality of cut and how well it mulches up most of the material compared to my rotary cutter. I would say I could probably cut through tall, heavy, weeds a bit faster with the rotary cutter but in reality my cutting speed is governed more by the rough ground and just watching what I'm going over. My RC hasn't been on since I got the flail.
Anyway I'm very pleased with the quality of cut and how well it mulches up most of the material compared to my rotary cutter. I would say I could probably cut through tall, heavy, weeds a bit faster with the rotary cutter but in reality my cutting speed is governed more by the rough ground and just watching what I'm going over. My RC hasn't been on since I got the flail.