The transfer case heat issue is treated like Voodoo by a lot of people. They know it is there, don't understand it and either ignore it or become scared of it. Each of us can only speak of our own experiences for the most part too.
Mine is like Jon's. Center output and sustained speeds above 50 mph cause really high temeratures. I don't have a gauge plumbed into it. Using my infrared thermometer the case on mine has gotten as high as 278 after driving with stock tires at 60 mph for 45 miles. This was while driving to the 2005 Texas FE. I had 180 miles to go and slowed down to 45. The case was between 230-244 the rest of the trip. Coming home I never got above 50 and the case stayed at 218-222 when I checked it in every town I passed through.
I don't think the center output helped me much in temperature, but it sure did get rid of the noise.
One year later, I towed a M715 behind my M715 to the 2006 Texas FE. I only checked the case once because I didn't even smell it getting hot. It was at 219. I learned my lesson and never exceed 50 mph indicated on the speedometer if I have to drive more than 10 miles.
It all comes down to what has already been posted. If you plan to turn the transfer case at more than 2500 rpm then it will probably over heat. If you let it get hot and stay hot, your seals will fail. Then all your lube will come out and you will have a really hot chunk of solid metal under your truck. Consider a driveshaft speed of 2500 as the t-case redline. 2200-2300 should be your normal cruise t-case rpm and right at the top of the "green" range.
Anything above that and you need a different t-case in 95% of our trucks.