I'm relying in part on Dan's post above, but I believe I looked this up some time ago. Even at 65psi, a 55psi tire would be closer than I'd like to see it. The 100psi stems make more sense to me, considering the cost.
I did just find this article which says 65psi, so I dunno for sure; if I'm wrong, it wouldn't be the first time for sure!
Here's a stem source posted on Yahoo Scampers showing 65 psi, so I guess 35 is wrong.
Items that can be considered to be a safety factor when a failure occurs are usually tested to at least double the rated pressure. Even non-safety stuff is tested much higher than published specifications. An example I know of is brake lines for air brakes
in trucks. A truck's air system is 120 psi, brake air lines are rated for 300 psi, we tested to 600 psi. My point is that even with a tire inflated to 55 psi you're probably a long ways from failure.
I don't know what the down side is of going to a higher rated stem, if there is any other than cost. Assuming that isn't any real down side, go to the higher rated if it will reduce concern.
are rated at 35 psi max, so I'm not gonna worry.