Cut his journey almost in half, add several hours of sleep, and reduce hard-man levels by at least 60 per cent and I know a bit about the challenge Mr Hopkinson has taken on.
In 2010, I shivered in driving rain after a night in a broken tent as I pointed my wheel south from John O'Groats. My destination: Land's End, via hundreds of miles of pain, weightloss, terrible tanlines and wayward sheep.
Hopkinson's 843-mile route each way is as short as it could be via road but must include soul-sapping stretches along thundering A-roads. My advice: ditch the stopwatch, take the slow road and gaze at glorious views that no other conveyance can offer.
My one-way route, drawn for the first Ride Across Britain, an annual event, took in 1,000 miles of lanes, climbs and thrilling descents. It took me nine days, an average daily ride of 110 miles (Hopkinson will have to push 280 a day, which is madness).
It was, in places, excruciating but beyond the pursuit of supreme fitness or the glory of a personal challenge, my ride wasn't just across a country but about one. As Ernest Hemingway wrote, "it is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them."
The American would have enjoyed my ride, which took in the banks of Loch Ness, the glorious Lakes, the undulating Cotswolds and windswept Exmoor. I only hope Mr Hopkinson has a few moments to coast, wipe away the sweat (and tears) and drink it all in.