I was in your exact situation except I bought a 2005 tiger cub with a 48" deck new in 05, and man was that a 7 year mistake. I could have upgraded sooner, but I really wanted to wait until i had more accounts and I did. I chose the 61" cheetah with a 34hp carb'd air cooled kohler motor, might not be the best of fuel, but i'll probably never have an issue with the whole mower. I demoed the mower when it first came out 3 years ago and fell in love with it. I really can't see how i went so long without it, I let my buddy use who works with me in the summer, and he's got an exmark and even he admits, he my scag is a beast and he really loves it. he like you and me went with a deck size smaller then 61" for his first machine. its a common mistake a good amount of people do. but it happens atleast you went with a used machine.
fully lic. and ins. 10yrs exp.