Just to add a little info here, I have a 60" flail mower that I use on my NH 29DA, which is rated as 29 PTO horsepower. In heavy wet thick grasses, it will bog down and even kill the engine if I don't use the clutch. In medium or light grasses, it cuts fine. But I feel that my 29DA is underpowered for this size mower. For a 60" flail, I'd recommend 45 horsepower or more. Not sure if a rotary mower takes less horsepower, but I think it does. The advantage of a flail is you can run over downed branches and debris and not hurt the mower - it just makes a lot of noise as it pulverizes the debris. Rotary Bush Hogs can take debris to some extent, but flails mowers were meant to take it.
The problem with trying to do half-width cuts in heavy grasses is the large clumps of cut grass that spit out will get caught up on the next pass and it will be as if you are cutting with the whole width of the mower. So doing a partial width cutting does help somewhat, but is not necessarily the best solution. I think its much better to raise up the mower and take full cuts. Keep raising the mower until you can get through without bogging down too much. And you can always lower the mower in sections where the grass is less thick. Plus, grass grows back quickly, so you'll likely get 3-4" per week and in no time its as if you never mowed it at all. So don't get too worried about cutting grass really low because it won't stay low for long. No matter how high up you cut, a cut field looks better than an uncut field.
The other trick is to mow when grasses are wet, in early morning, seems to act like lubricant and is easier to cut. In late afternoon, the cutting seems harder.
Also don't forget to try to offset your mower, if possible. If you can make it stick out past the tires (usually on the right side) it will make it easier to get into corners and cut along fences. But it also is cutting after your tires have flattened out the grass, so offsetting usually means you can keep two tires on already mowed grass and only flatten grass with the other two tires. So that helps a bit as well.
Overall, mowing technique makes a big difference on how much horsepower you need. Having lots of horsepower is nice, but you can get by with less if you adjust your technique. Less horsepower generally means less fuel, and less tractor, and less cost. So you can save a lot of time and money with good mowing techniques.
My blades are sharpened more like a mower than a rough cut and it does a neat job.
