The problem will probably not be the
PTO hp. The gear box rating has more to do with how much hp the gear box can handle, not how much hp is required to run it.
What you need to look at is the weight. The L4400 is only rated to carry about 880 pounds on the 3pt hitch. I know that people have put more back there without any problems but I wouldn't exceed a 1000 pounds.
I could not get the specs to come up on that cutter but it looks pretty beefy. Why do you need that much cutter? What is the weight on that model? How big a tree is it rated to cut?