A couple of months ago I hit 55; wasn't really planning on it, but the downhill was wide open, with no traffic, fairly decent surface, and plenty steep enough (parts of this road exceed 13%). I was in a tuck, knees and elbows in, hands on the hoods (I think). I can't say that will be my maximum speed in the future, but I won't rule out exceeding the "double nickel"; just depends how I'm feeling (a couple of weeks ago on the same descent I barely broke 50) and of course the conditions.