I...spent over 600 miles on the road in a car scouting roads for a new 600k last weekend? (yes, miles, because a: scouting multiple options and b: had to come home as I couldn't get it all done in one day) That was not quite as exhausting as riding a 600k, but I am never leaving things late enough that I have to do that much scouting at once.
(I'd hoped to scout it on pedals as a three or four-day tour, and should probably have done that instead of attempting the Waterfalls 1200k, but hindsight is 20/20.)