I just purchased a gravely 54" ztr with a 24hp kawasaki on it and its awesome!! Kawasaki engines are the way to go no matter what you buy. Kubota's are great but their cheapest one is about $8,000. Any mower that will go 13mph will cost ya about $10,000. I was going to buy a toro with the kawasaki engine and fabricated deck but they're having trouble getting them in. Another thing to consider is what hydraulic motor is in the mower(look for ones that have a fan on top). The cheaper ones (with no fans) are throw-a-way type and can't be fixed. What ever you do stay away from briggs and stratton engines.