Well, this should be a nice short thread :)
The only way to answer the question is to get an accurate weight on the 5th wheel and truck both loaded up how they will be when you travel. If it's within the specs of the SRW there you go. There are a lot of folks on here who don't believe it's safe to tow a huge 5th wheel with a SRW even when it's within the ratings of the truck. Personally, if the truck's rated for it I see no problem but everyone's entitled to their opinion. If you're looking for people to tell you everything is going to be okay towing with an overloaded SRW truck it's probably not going to happen here.
Being a pretty firm anti-dually guy myself I'd probably look for a smaller trailer if it didn't fit with the SRW.