With either one you'll crawl up the grades. I'd guess 35 MPH on 6%. They are not designed as rocket ships.
But it's about torque and not HP, so look at that. I went from 350 38' Endeavor to 400 42' Scepter/tag and there was no difference on grade due to weight. The tag is however much more stable for passing, wind etc. At say $600/tire and maintenance you pay more. The rear overhang is greater and you lose about 3' of outside storage on both sides.
The Monaco chassis like many has compromises. Driving fatigue can be one and some have installed additional equipment for that purpose. I would not buy the non tag one unless both front and rear Watts links are available in case you decide later for that one. But maybe the Dynasty is better set up as I have no experience with it.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland
Bob