Fastest - 56 mph. I was going for 60 down a steep hill but I hit a raised drain cover. I was looking down at the computer at the time so I didn't spot the hazard ahead. I chinned my handlebars and almost bit the end of my tongue off, and I got big air. The bike bounced back into the air when I landed and I almost went under the wheels of an oncoming vehicle. It wasn't my proudest moment on a bike, but it was one of my scariest ...
Slowest - I bonked on the last long hill of a tough local audax (randonneuring) ride and was absolutely grovelling my way to the summit. I looked down at my computer and saw that I was only doing 2.7 mph. Eventually, I remembered that I had set the computer to metric for the event because the route sheet was in kms. I was in fact doing a mere 2.7 kms per hour - 1.7 mph!