I have an 7ft. Woods mower that I pull with either a 35 Massey (35 horse) or a 231s Massey (45 hp). Either one works great. My neighbor pulls a 6 foot Woods with 20 horse Yanmar. I think he's under gunned, but it seems to work for him.
If the pastures get out of control I go to a 6 ft. Massey bushhog.