I have a mechanical heart valve and thus take blood thinners daily. As such, I try to keep speeds down on descents. And extra 5 or 10 mph isn't worth it to me.
Last summer I actually got up to 39 mph on a loaded touring bike heading down from Virginia City Hill to Ennis, MT. That was very fast for me. I usually limit my top speed to 30 or so. The only reason I let it fly that time was because there was no traffic, the road was straight at that point, the surface was good and I was in full sunlight. Riding a tank like that with its relaxed geometry and 37c tires also makes you feel quite stable and grounded. You just have to be prepared for crosswinds. That day, I was going straight into the wind. Imagine what I could have done with the wind at my back.