It all depends on your age and whether you are going full time or just using it once in a while.
If you are not a full timer and you are retired but wanted for an outing every once in a while I would not go much more then 36-40' diesel pusher. If you are planning on full timing THEN go 45' if you can afford something like that, because you got to realize that if you are selling your stick house and lets say it is around 2K square feet, all of a sudden you are going to drop to 400 sq ft average. It is sometime a shock to both you and your wife.
I myself like plenty of room that is why I keep my stick house to fall back to every once in a while.