I mow about the same amount and went with the 61" for the same reasons you are considering. I can store the 61" inside, limited scalping, and can get in between trees better. I have no regrets not getting the 72". I went with the fx921 as an engine choice. I cannot comment on the Kohler.
The prices quoted are reasonable. You can probably find one for a few hundred cheaper, but if its a good local dealer, go for it.
I don't mind spending money, I mind wasting money!