I have used 1" square aluminum tube as well as 1" round tube as load bars for my Yakima...

and

The square tube was MUCH better then the round, for sure. But still felt a little weak to me. I also used rather thin aluminum.
Well, scouting out some options, I came across a set of THULE load bars on craigslist for dirt cheap.

First impression... although a little worn, as they are used... these things look good. And man are they STRONG! I haven't mounted my rack to them yet, but I'm planning on doing so soon. I also have an idea for mounting to the tracks... that's staying top secret for now, at least until I can confirm/deny that it would work...