Agree.
I've used both tractors in the same conditions. The 59 is more sure footed in steep uneven terrain. While I had tire ballast on the 39 the 59 doesn't seem to need any.
I figure the added 59's weight and wider track lines it out better.
All these tractors are expensive. My opinion is you might as well get one that does just about any job you need doing. I feel the same way about trucks. If you amortize the cost difference over 10 years you might as well get the bigger tractor.
I sure can't go to town for help and my neighbors count on me too.