Pretty sure you are looking at the difference between either the shortbed at 15k and the long bed at 17k for the F250 4x4 configuration.
In any case, the diesel engine won't care if its 15k or 17k back there.
The truck won't care if it's carrying 2100 or 2400 lbs. The lawyers probably might, if you get into an accident.
If you care about lawyer numbers, get the F350 for an extra $1000 bucks to cover that.
Payload ratings on tires are more important than some covering posterior end lawyer payload numbers. Tires are made of rubber, which can heat up and pop.