I just got my stand powder coated and it is supposed to be good up to 1200 degrees. I haven't brewed on it yet, so I can't say if it is holding up (but hopefully this weekend).
What size kettles are you going to use? With 18" opening between beams, you may have a lot of heat wash coming up the sides of the kettles. This can cause issues with sight glasses, valves (seals) and tubing.