I agree that there are many, many factors involved with towing. Even environmental conditions (such as ambient air temperature) plays a huge factor. In fact, engine/system cooling was one of the obstacles that the Jeep engineers had to overcome to get the JT tow rating over 5000 pounds (if you look closely at a JT, the grill spacing is larger on the JT than it is on a JL). Heat testing (on different sub-systems) is part of the SAE J2807 (and other standards) towing standards.Sorry, not how it works. It's not "can it move it". There's a whole lot more to the equation. Too many try to over-simplify it. It's not about it can or can't move it, it can or can't pull it. It's about heat, axle ratings, braking, engine load, gearing, just a whole lot of things considered.
You are trying to make it all about weight and it's not. If it was, then if you removed 200 pounds of weight from the truck, it could pull 200 pounds more in a trailer. Or if the trailer was 200 pounds lighter, you could put 200 pounds more in the truck. That's not really how it works.
>>I have never heard how differential gear ratios affect suspension - I am a licensed engineer, but that is a new one on me..... <<
Gear ratios don't impact suspension - but you have to consider that the Overland has NARROWER axles. Sport S max tow and Rubicon have WIDER axles, besides the lower ratio. The wider axles DO impact how it handles and what the tow rating would be.
>> I will be atleast 1000 pounds under tow capacity, atleast 1000 pounds under GCVWR, but maybe marginally over GVWR of the JT. If I dont like the ride, I may try adding air bags to the back <<
Over weight in the vehicle - over GVWR - then you get into issues - legal and otherwise. Again you are trying to make it about ride, comfort and height - it's not about comfort. You are looking at it wrong. You can't resolve that with air bags!! If you are over, you are over. IF it was so darned simple a person could add heavier springs - and that will NOT help you carry more weight. You can't add air bags and be legal.
I agree, every pound of weight over a GAWR does things like increase "system" coefficient of friction, which in-turn will generate more heat, which in turn will cause the axle grease to break down faster, which in turn will cause the coefficient of friction to increase, which leads to a exponential failure mode of the axle. But, there are soooooooo many more variables to get there, than just the weight on the axle. I know I would rather drive on a new (or almost new) Dana 44 axle at 100 pounds over it's weight limit, than a non-maintained 20 year old much heavy duty axle operating at half of it's GAWR. Pretty sure we can predict which one of those axles would fail first. BTW, my JT Overland front GAWR is 3100 pounds and the rear GAWR is 3750. I am pretty sure I will be well under both of those axle ratings.
It is obvious that we will never agree on any of this. At this point, it is moot to even discuss it.