My CK35 lifts motors just fine, and I pull a 5' rotary cutter with it with no issue. The 25hp tractors I am considering have roughly the same weight and lift capacity, so i'm not worried about it being able to lift what I need. My question was more around the HP requirements of a flail mower, and how that compares to a rotary. From the comments it sounds like I need more than 25hp to run a 6' flail, so I'll look at models with minimum 30 pto HP and just deal with the emissions.
Now that minimum HP has been decided I need to decide if I want to stick with a unit similar in size to my CK, or step up to the next size up. A big consideration there is that my wife will be doing some of the mowing and other things with the tractor so I'll have to get her comfortable if I go larger. So I'll be looking at the Kioti CK4020, or lowest HP DK/NS/NX model, and Yanmar YT235 and YT347, and the equivalent sizes in other brands.
I dropped my old CK off at a dealer today for a clutch replacement, something I would do myself if I had space and time. This is my first dealing with this dealer so we'll see how it goes. They carry Kioti, New Holland, and Massey Ferguson.