I find the only cycle that doesn't cause me pain, is my motorcycle...
Otherwise, it is just a question of what will start hurting first. I guess the goal is to have my legs give out, but honestly, I like to have some kind of early warning before my legs cramp up, and I have to call the meat wagon to haul me home.
But I am definitely considering a bent, when they pave the road in front of us, till then, I will make due with a hardtail...