I have a D990 and bought a JD MX5 rotary "bush hog". It does an excellent job on the pasture, and cuts small brush. I have also used to mow my front yard, which I usually mow with Woods finish mower. I also did an excellent job on the nice grass. The only problem I have found is when turning a sharp 90 to the left or right, the side of the mower deck tends to dig a bit into the dirt. To get around this, I now lift the mower a little bit when turning, set it back down after the turn and keep cutting. This being the case, I can't go in a continuous circle, but rather back and fourth. I have not found an eay way to sharpen the blade, though, but the blade is very durable considering the rocks I have hit in the pasture. I got most of them out now.
The smaller rotory bush hog type mowers like the MX5 have two blades attached to a centered steel hub. The are attached with one big bolt. If the blade hits a rock or log, it simply swivels.
The finish mower has sharper blades, and one lke mine, a 5' unit, has three blades connected by a single belt. The MX5 is gear driven. The finish mower is for fine grass and if you hit a rock, it can take a good chunck out of the blade. Usually you can get a closer cut with a finish mower also.
A flail mower is finer yet, as I understand it, these a good for golf courses, but I could be wrong on this.
I think for your application a bush hog, like the MX 5 or MX6 would be great.
I had a JD 790 before I bought the 990. The 790 did a great job handling the MX 5, no problem at all. But I also have a FEL on it for counterbalance.
I bought the 990 because I needed the lift height to dump into dump trucks. I hope this helps.