Hopefully this helps, I made a quick breakdown between the past few years Super Duty's and there is a difference between regular 250-350's regarding axles etc. They don't have the same.
This info was pulled directly from Ford's fleet towing information and I just copy and pasted the info.
So the f250 axle is actually rated at 6200 lbs springs or not, air bags or not. That is what you should actually go by. Weigh the truck and see how much weight is actually on the rear axle then add your pin weight and you'll know if you are over or not.
Just again, the springs or air bags or whatever you have back there only support the weight from sagging the rear of the truck down. That's all. They don't increase towing capacity.
Also I'm not saying the truck won't be able to pull the weight. The engine transmission and frame are more than capable, all are used up to the F550 but from a technical standpoint. The rear axle is the main difference between each and super duty model.
Edit:// Ok so if you have a 2011 f250 here is the info on Ford's site, just scroll down to page 73 for rear end info.
https://www.fleet.ford.com/truckbbas/topics/2011/2011_SD_Pickup_specs.pdf
2011 Model Super Duty
F250 SRW"Sterling" axle rated @ 6200 lbs___springs rated @ 6100 lbs--axle shaft dia 1.36"min - 1.50"maj - 35spline__brake size--13.39"
F350 SRW"Sterling" axle rated @ 7280 lbs___springs rated @ 7000 lbs--axle shaft dia 1.50"min - 1.57"maj - 37spline__brake size--13.39"
F350 DRW"Dana 80"axle rated @ 9000 lbs___springs rated @ 9000 lbs--same as above__brake size-13.39"
F450 DRW"Dana 80"axle rated @ 9000 lbs___springs rated @ 9000 lbs--same as above__brake size-14.53" front - 15.35" rear
F250/350/450 front axle rated @ 6000 lbs for 4x4 - 5250 lbs for 4x2 -- all brakes above are rear sizes front are 13.66" except F450
The actual axle housing diameter is the same 3.5" on SRW 250 AND 350. 4" diameter on F350/450 DRW.
2009 Model Super Duty
F250 SRW"Visteon" axle rated @ 6200 lbs_______springs rated @ 6100 lbs---axle shafts same as 2011/model
F350 SRW"Visteon" axle rated @ 7280 lbs_______springs rated @ 7000 lbs---same as 2011 F350
F350 DRW"Dana 80" axle rated @ 9000 lbs______springs rated @ 9000 lbs---same as above
F450 DRW"Dana S110" axle rated @ 11,000 lbs___springs rated @ 9500 lbs---same as above
F250/350 front axle rated @ 6000 lbs -- F450 rated @ 7000 lbs -- all brakes are same as 2011 models
The actual axle housing diameter is the same 3.5" on SRW 250 AND 350. 4" diameter on F350/450 DRW.
2006 Model Super Duty
F250 SRW"Visteon" axle rated @ 6200 lbs_______springs rated @ 6100 lbs---axle shafts were same as 2011/model
F350 SRW"Visteon" axle rated @ 7280 lbs_______springs rated @ 7000 lbs---same as 2011 F350
F350 DRW"Dana 80" axle rated @ 9000 lbs______springs rated @ 9000 lbs---same as above
F450 DRW"Dana S110" axle rated @ 12,000 lbs___springs rated @ 12,000 lbs--axle shafts dia 1.72"min - 1.85"maj - 34 spline
F250/350 front axle rated @ 6000 lbs -- F450 rated @ 7000 lbs -- all brakes are same as 2011 models
The actual axle housing diameter is the same 3.5" on SRW 250 AND 350. 4" diameter on F350. 4.25" on F450