I've been reading about the doom and gloom of lawsuits for being overweight etc for years on this forum. I have yet to see a single post citing where it was leveraged in a liability suit. Not saying it doesn't happen but I've never seen anyone prove it despite the numerous claims. Willful negligence is very difficult to prove especially in an accident where so many other factors are involved. It usually comes down to failure to avoid an accident rather than willful negligence based on equipment. It would have to be pretty gross negligence. Any attorney worth his salt will take the path of least resistance and pick a strategy that is more easily understandable by a jury. I would imagine being slightly over your payload is never the primary cause of an accident for 3/4 and 1T trucks towing FW's. I encourage anyone to provide a case where this happened and put some teeth to this argument that continually shows up on this forum.
That said, numbers don't lie. If you run the numbers on the truck and trailer loaded for travel, they will tell you if you are overweight. And that's a factual and mechanical approach. Your equipment could fail or at least accelerate it's demise and performance could be affected. Is it the end of the world? No. I see clearly overloaded PU trucks daily leaving Big box stores.
The F250 and F350 are pretty identical with the exception of payload. You can buy add on equipment that is OEM that pretty much makes a 250 into a 350 with upgraded springs etc. It's a factory option - which always has me question the purpose of the F250 in the first place. Same price, can make the same capacity, etc. To each his own.
In it's current state with the current FW, loaded for travel, Your combination you are proposing appears to be overweight.
You can take remedies to try and compensate. Look at a smaller FW, get the proper springs, get a new truck, or roll the dice. Those are really your only options.