I have an older B7100, 1983, manual, and I picked up a 42" brush hog just last summer. It works great! I was just using it last week to clear some trails in the woods as part of someone's forestry plan. It is rated to cut up to 3/4" brush, but it easily handles brush a little larger. I also like it because it is the same width as my back tires. I think I paid $800 new.
teach
I bought a King Kutter 48" rotary for my B7100 and it worked just fine. Heavy grass (3-4ft tall) just means you have to slow down a little bit. I didn't have any attachments for the front of mine so hills made the front end pretty light, but caution got the job done.