I finished my 400km brevet, keeping good nutrition throughout, etc. But it wasn't enjoyable at the end, at all. After 200 miles, I'd felt I'd had a nice scenic ride and was ready to call it a day. Last 25 miles sucked, and I promised myself I was not going to do the 600km I'm signed up for in June. I'm not quitting randonneuring, but count me out for anything longer than a 400km, and even that I'd only do once a year I think. 300km is probably the sweet spot for me.