My guess it depends on how it is loading it.
If you are on loose wet pavement or grass (ahem) there should be not that much more of a load as compared to dry pavement sort-of 'extreme' conditions. The rear end may get pretty mad...but I think the transmission would only be unhappy if it got shocked, or your motor mounts if you were doing power brake take-offs...
One day I was trying to listen for a "under load" noise, checking boost, etc so I was powerbraking in gear and had the hood open
After you see the engine nearly turn itself upside down in the bay and push/pull on the motor mouts, you stop the power braking.
I just save that action now for showing up cars off lights, the taco time parking lot, and sometimes a power slide.
I have to agree though, these do feel comfortable sideways. I am sure the sidewalls hate the treatment however it feels a lot more solid than say, my 69bug haha
But the Mild Terrain tires on that make it grab a bit too much.

My advice, avoid power braking...lest you already have bad motor mounts...I cannot belive how much that engine moves!

(But taking off at 2100RPM in the boost curve, high tourque and horsepower is fun....hmmmm) :p