I don't really do BIG MILES, but I have a nice run out to my in-laws near Brecon that's 70 miles .
It's just long enough to feel the tiredness and just hilly enough to remain interesting.
In a stately, middle-aged way, 3 hrs 45 is my best recorded time on a road bike.
The Brecon Beast charity enduro is about that length, but much, much harder.
I refuse even to put my best time on here for fear of being revealed as a fake off-roader.