Burg,
I don't generally disagree with most of your post, but a couple of points...
Your "cargo" weight calculation is pretty excessive. 500lbs of cargo/misc? 1/4 of a ton in ice chests and picnic baskets? Maybe 200lbs, and if only two people that adds back 650lbs to the tow rating, which puts you back in the OK range to tow that boat. Also, remember that the tow rating manufacturers give is conservative. You vehicle doesn't magically blow up if you exceed the rating by 100lbs.
Also, the size of the brakes on the Boxster isn't so it can stop once, but rather so it can haul the car down under severe braking (racing) repeatedly without fading. Got to dissipate that heat, you know.
The Explorer is not being asked to do that, so it can do just fine without having massive brakes. It's brakes can survive a couple of panic stops without fading, and if you're towing, why would you be putting yourself in situations where you're repeatedly pounding the brakes? If your towing 6000lbs, you sure better be planning ahead, leaving stopping room, etc.
Besides, a 3 ton boat and trailer better have it's own set of brakes. If you're towing that without trailer brakes, you're taking a huge chance and probably breaking the law.
Finally, the trannies will last 150k or more. Heat kills transmissions. An external tranny cooler and fluid flushes every 20k or so does the trick.
Oh, and my last Explorer went 64k miles on it's
original set of pads. A new set of pads and it was good to go on the
original rotors. I've heard other Explorer drivers say that they go through brakes just like you describe... what are you guys doing to your brakes?
In the end, an Explorer's towing downfall isn't it's capacity, but rather the short wheelbase. That's why you can "feel" even lighter trailers back there, and that plagues all short wheelbase tow vehicles. If you're towing relatively short distances on flat land, that Explorer and trailer brakes will do 3 tons just fine. Long distances or mountainous terrain, I'd want an F250/350 sized vehicle.