I've done a lot of spreadsheet work, and for a 5vr, the limit is almost always the payload. For a tow behind, it is almost always the hitch capacity. There is a gray area with payload on the 3/4 tons, in that the 10,000 lb. GVR seems to not be directly related to the other technical parameters like axle capacity, tire capacity, etc. , but more likely driven by the DOT requirement for commercial drivers. It is clear that many, many people tow with "overloaded" 3/4 or even 1/2 ton trucks. After much internet research, it isn't clear whether there is any attempt to enforce the GVWR, but some people think there is an insurance/lawsuit exposure. Since I was buying a new truck anyway, I just went ahead and paid the extra for the F350. However, unlike the message from many on the forum, I found considerable price difference, due to the discounts/rebates on the F250 that were not available on the F350. Also, the color, equipment combinations were much more limited on the F350's in stock.
2010 Rockwood 8280WS Fifth Wheel
2013 F350 Crew Cab SRW, Standard Bed PS Diesel
Reese Airborne Pin Box, Reese 16K Manual Slider
Camped 28 Days in 2012, 23 Days in 2013, 29 Days in 2014, 30 Days in 2015, 9 Days in 2016