I tend to use mine more to transport the odd home depot dimensional product or steel from IMS. That being said, I have found times when I threw stuff up there. Stuff that you don't want in the cabin, like gasoline, wet clothes, etc etc. or lightweight stuff like empty water jugs, chairs, tents, etc.
400 pounds dynamic load (that is, 400 pounds of stuff going down the highway) is way excessive, and IMHO dangerous. 150-200 is the max I would ever put up there, depending on rack weight.
Here is my thread:
http://www.ultimateyota.com/showthre...w-Profile-Rack
I have been very happy with the 1"EMT. It's close enough to 0.60 wall tube that it doesn't matter. The load bearing cross bars used 3/4" RMC, which is nearly the same OD and has a wall thickness around 0.100. I am actually surprised how rigid the rack is once it's all welded up.
I will eventually toss my RTT up there, and that would be the heaviest thing I would ever put on the roof.
If you want my solidworks files in something sketchup can digest, let me know. I never completely finished them, but they are a decent starting point. Solidworks reads it out at ~40 pounds, so it is probably around 50.