A link to your Garmin Connect with mile splits would work, or perhaps a link to the Strava segment. If this is a popular climb, I'd wager there's a segment setup. And if you're that fast, you certainly must have some sort of GPS device you're using.

I cruised downhill at 35 mph yesterday...kept up with some motorcycles for a while. It was kinda cool. But I certainly was much slower after turning around.

But really, you're very lucky it was a nice guy. I'd never do something like this.