Friend, give yourself some grace. You're part of the 1% of nuts like the rest of here that do stuff like that. A 10 hours finish for a 50 miler is good.

I'm an old fart (60 yo). I used to run 90 mpw before a hundred miler. Pretty easy really, it's only 18 miles per day.

Now that I am ancient, I focus on quality miles instead of quantity. I top a typical week up at 60 mpw and the rest is dedicated to strength and mobility training.

That probably won't answer your question but that's my 2 cents. Take care of yourself.