jlgail, in case you haven't seen it yet, Tirerack has a spec sheet on your tires.
You just go to the following link, and hit the "specs" button.
As you can see, the load rating is 2094 lbs at 65 psi.
But what surprised me is that it has an "R" speed rating, which is 106 mph!
So, it would seem that if you want to cruise at 70 down some hills, you should have a fair bit of safety there.
So you have a safe cushion not just in load capacity, but speed as well. That is what we should be getting straight from the factory.
JMO, of course.