6x200? Do you mean you did 6 200k rides? Or a 1200k?
I only get out of the saddle to stretch and recruit different muscles, more often when climbing, like every few minutes. It's different with everyone, though. I rode across my valley alongside a local pro and he stood up the whole way, ten miles or so, and I was pushing myself pretty hard to not bore him too much.
I climbed a 9 mile canyon with another club rider and he stood all the way. Some people are comfortable standing for long periods.
A friend had long term numbness in his hands after his first 400k, I think, in the mountains. I get a little numbness after lots of descending and squeezing the brakes, especially when it's cold.
The 6X200 was 200 k per day. Much nicer that a 1200 k continuous.
Younger riders can stand for long periods. I haven't seen many older riders stand that much, if any.
In my opinion road surface affects the arms and hands specially when yr on the downhills.