From what I've seen, the problem has more to do with overpacking or using heavier than necessary gear than a limitation of the bike. If your cargo weighs more than 50 lbs (being generous), there are usually opportunities to drop weight.
Before you decide which bike you need to decide how much shit you plan on packing for the trip. While a 450ish thumper is a great choice for the terrain it’s ability to carry a lot of gear is lacking.
Just something to consider.
I did 9 days across New Mexico, including the NMBDR on a CRF450L, fully loaded. a huge plus of the CRF is a robust Alum Subframe.
All in, me + gear, I'd say 350# of stuff on the CRF. No issues with hauling stuffs.