*I've had my 455 for a little over a year now. I have added a 3 point hitch and PTO and work it almost as hard as my 4410. The thing sips fuel. If all I did was mow an acre twice a week, I don't know how long a tank a fuel would last. But, I am always dragging a trailer full of mulch or running a roller pump or using the front blade to finish grading where I can't get with my 4410 -- so I have to fill it every 5 or 6 weeks.
When I mow, it is WOT with a 60 inch deck and Power Flow MCS mowing right at an acre -- and I usually cannot see a change in the fuel gauge from start to finish.
Unless the dealer beats you up on the trade, or the 455 has been "rode hard and put away wet", I would jump on it.