F450 has more towing capacity per Fords towing guide. Conventional towing (bumper pull) is the same , this is due to the certified rating of the hitch/ball and is 21,000lbs with a weight distributing hitch.
5th wheel towing is strength limited to 27,500lbs
goose neck would appear to have no limit.
The max a 2017 F350 SRW is rated for is 18,000 bumper pull. 21,500lbs goose neck
F350 DRW is 21,000 bumper pull. 32,000 lbs with the right gear ratio and bed delete.
F450 is 21,000 bumper pull (again limited by the rating of the hitch/ball) with 32,500lbs being the limit for goose neck. No special options like gear ratio or bed delete required for F450. You get a F450 and it just does that, you want your F350 to almost be a F450 you had better choose set up/options wisely.
for 2020 the difference is even greater.
PS. I don't really consider any towing specs prior to 2015 to be legit. It wasn't until about that time that there became a standardized test and independent certification.
Check out the new standard in tow tests, the SAE J2807. See how this new HD truck testing will level the playing filed when it comes to testing the latest Trucks
www.trucktrend.com