I have the stealth, not the full height rack, but I may be able to help. The Stealth comes with the 2" brackets and the rack sits about 1 1/2"s above the roof. At around 245lbs I have no problems walking around and shaking the truck side to side. It makes sense that with the taller brackets and the rack sitting on the stock crossbars you would have better strength. I could not find weight ratings, but doubt it would be an issue.
Look at all the crap on Adam's truck (
) in this thread. He has the 2" brackets.
http://elcova.com/groupee/forums?a=tpc&s=2826088551&f=5106011751&m=524106199