The E450s all have the V10 with 4.56 gears, and starting with 2016 models (chassis model... the coach is sometimes a model year newer!), come with the 6-speed TorqueShift transission.
Really, I think some folks are overthinking this too much. The E450 (Class A or C) or the F53 Class A can all handle that size trailer, and perform adequately while doing it. It just may require keeping the rear cargo holds empty, to give up that weight for hitch weight.
I do see the appeal of having two separate RVs. For the majority of trips, being able to take only half the combo would be really nice. Plus, double the water capacity, double the bathrooms etc.
The bigger issue I see is hitch clearance. Many of the shorter TTs have a short tongue. You'll need a 4' tongue to keep the TT from hitting the motorhome during sharp turns. But there are some lightweights out there with a longer tongue. Just depends on make.
Weight distribution will be wanted, if anything just to prevent porpoising over bumps. If you get a motorhome with a high wheelbase to length ratio, sway control will not be needed. And that ratio is important for good handling anyways, so its something to watch out for. And... could be a good reason to go slightly larger on the motorhome. The longer motorhomes ofter get all the extra length in wheelbase (shorter coaches get shorter wheelbases, to keep wheel-wells out of the bedroom)
