I am like Mark, I have a 38 hp (35pto) tractor and use it with a 6' woods brush cutter. It's always been fine, unless the stuff is real thick. The biggest problem with mine is not so much cutting it, but getting rid of it. It seems to be too restricted coming out of the hole in the back of the deck, though it does chop it up well. The other problem with mine is selecting a speed. It is gear drive with 3 ranges and 3 speeds within the ranges. The problem is for most mowing I can do 4th gear, but have to occasionally switch to 3rd which requires a range change and therefore having to stop the tractor. The difference in speed between 3 and 4 is almost double so I don't want to stay in three unless I have to. Makes for a lot of work- it's one time I wish I had a hydro tractor. But back to your question, I don't believe you will be under powered at all with a 5' bush hog, just have to slow down sometimes in thick/ tall vegetation.