Hopefully I don't ramble here. Since I first started RVing in 2003, every towing guide I have ever read states 15 - 25% of trailer weight. Those stated percentages are to allow for safe acceleration, towing and braking of the tow vehicle and trailer combo.
Not enough pin weight means not enough weight on the tow vehicles drive axle. The tow vehicle will be trying to pull more weight with less traction. Less traction affects acceleration and braking. Ever notice how a dually rides and brakes smoother with weight in the bed ? At least mine does.
Too much pin weight stresses the tow vehicles suspension. It also takes weight off of the tow vehicles steering axle. The front end starts feel like its wandering. Not what you want in an emergency situation. Less weight on the steering axle also affects braking. The larger brakes are on the front and with less traction on the front, less braking power. Now you are hoping the rear brakes, with overloaded axles will stop your truck and rig.
Do the math according to your tow vehicles weight ratings. GVWR, GCWR, Cargo Capacity. If your truck has a GVWR of 14,000lbs and the actual weight, loaded for a trip, weighs 9,000lbs, then you have 5,000lbs remaining Cargo Capacity. The 14,000lbs is the max weight at which your truck can be safely driven. The 15 - 25% pin weight puts enough weight over the trucks rear axle to allow your truck to be safely driven pulling 12,000 - 14,000lbs behind.
The numbers you provided appear to be fine. (although you did not provide truck ratings) As long as you NEVER exceed your trucks GVWR and GCWR and your RVs GVWR, you will never be in trouble with a 25% pin weight. Do remember that the more weight you add to the front storage, the higher the pin weight. DON'T exceed your maximums. Redistribute or carry less.
BTW, most of the folks here that post their weights seem to be in the 20 - 22% pin weight range.
Now with all that being said, if you are actually asking how many pounds is too much for the front part of the RV frame...I'd say "when the floor collapses".
