The other side of things is regardless of what we feel we can tow or what we have proven we can tow, it all comes down to what the people selling you your insurance and enforcing the laws think.
And if your truck is out of compliance or illegally towing or overloaded, then you open yourself up to a rather numbing law suit should someone get hurt by what you are doing.
Unless you have nothing to loose, I would recommend following at least closely the requirements as well as the recommendations.
I know for sure, that if was hurt, or if any of my family was injured by a illegal truck, out of compliance, illegally modded, overloaded truck or some yahoo pulling a trailer heavier than recommended or faster than the tires were rated for (ST tires max at 65mph) I would use every tool within the law to extract as much payback for the others blatent disregard for the law / rules, as well as showing a caluos disregard for others saftey.
Really, the above examples are not "accidents waiting to happen", "or just something that just happened", they are choices that were made that can cause injury and death, certainly not a accident, a choice. And for what, just because someone cannot follow the same rules that apply to all of us?
If you need a truck with a certain rating, then do the adult thing and go out and rent or buy a suitable truck. Trucks are cheap right now to boot!
Just my two cents,
90 F250 7.5L E4OD, 03 F350 SD auto with the infamous diesel 6.0 for work, 70 C600 330 MT40 auto dump truck O2 Oldsmobile Bravada, Kubota L3200, Hustler Super Z mower, all Hydrostatics, 85 Honda Elite 250 & 150 scooter CVT - Nary a manual in the fleet!