I'm only at 32' but haven't had any significant issues. I think you'd really appreciate the way a fifth wheel tows compared to a TT, and you can figure on being about 4' shorter overall compared to the same length TT.
Don't let some of the weight police comments about your truck derail you - stay within your axle and tire ratings and you'll be good to go. If you do find more sag than you like you could easily fix it with bags or timbrens. There's obviously a point where the trailer size will dictate a DRW, but there are lots of bunkhouse style fifth wheels available that are well within your wheelhouse.