I did my first double last year. My ascent the second day was only 10 minutes slower, yet I actually felt much better when I reached the top.
The ascent works your muscles a bit, but mainly cardio, which is much easier to recover from overnight. My strategy is going to be to go all out on the PPA. I will focus on stretching, a bit of massage, refueling, and lots of rehydration through the rest of Saturday. I expect my time to be pretty close on Sunday. I found that I really enjoyed doing the ascent part 2 days in a row. How often do you get to run the same race the next day? The descent feels like a totally different race.
I wouldn’t hold anything back unless you’re looking to squeak out a couple of extra minutes on the marathon. Your joints and connective tissues should be fine Sunday morning. The main issues are definitely refueling and hydration. If you’re that concerned about it, then do only one race, otherwise. Let loose both days and have a blast!