I have a GT225 (pictured below with 42C Deck), which I bought brand new in 2001. It has been a great machine overall, but I live on a hill and mow an acre. The 15HP Kohler Command is a little bit weak for my size (I'm 6'6" and weigh 310) and the hills, and it bogs down frequently. I have my eye on the 455 with the 22HP Yanmar Diesel. What should I expect to get selling my GT225, and what should I expect to pay for a 455 with low hours?