I've spent most of my time over on the toy hauler forum but since we've been talking about moving from the TH to a diesel pusher this is where I'll ask my question. We've been looking at 34 to 36 feet...
The "rule of thumb" for DPs is 10 HP per foot. There are several 500 HP 45 footers out there and you may win the race to the top of the hill, but they catch up when you stop for fuel.
Stopping at 2008 also gets you in prior to the DPF/DEF era.