How do you people hit 50+ on these bikes. I've hit 39-40 on 1.10x26 slicks with 44x11 gears on a very long downhill but couldn't pedal anymore. I remember a similar thread about how gast you ride on the flat and some of the speeds people came out with meant that they rode 20% faster than Lance has ever ridden. I think you all need to check your computers.
Yeah, there are a few fibs on this thread, no biggie. (As an old stayer and derny racer, I'd like to know what gear was on the bike of the fellow who claimed to have done 65 MPH behind a Goldwing...

)
As others have more-or-less pointed out, though, gearing doesn't matter on the downhill. On a steep enough descent, aerodynamics becomes the whole ball of wax and if you can get enough of your fat arse out of the way, you'll go fast. Nobody's pedalling at these speeds unless they've purposefully selected gears for it. (You'd be amazed at the size gears necessary to pedal at 65 MPH...)
At any rate, there are mountain roads in Northern and Southern California, and in Colorado, where I know for a fact that one can exceed 60 MPH. I am sure there are similar roads in many other states that I haven't personally been on. Tell the truth, I don't really see the "bragging rights" of going fast down a hill. Gravity did all the work; all the rider did was, well, nothing. Didn't pedal, didn't brake... you should be just as proud for sitting on the toilet and reading Bicisport.