8’6 5wt. I don’t own a 9’0 5wt but that’s probably the most common middle of the road answer you’re gonna see, and if I owned one, I’d likely fish it on Penns some.
For Drakes specifically, I fish a 9’0 6wt. Can get away with heavier tippet, and less line twist when casting those monsters. And if I know I’m likely gonna be nymphing all day (I’m probably not going to Penns at all in those conditions usually) I’d use a 10’0 5wt. All of those rods are versatile enough that they could switch gears if they needed to, but yeah, if you made me fish Penns all year with just one of my rods, I’d pick the 8’6 5wt.
Edit: No right or wrong, but I only want to carry one rod at a time, and as such, I tend to prioritize versatility in my rods, over super specialized ones. Realistically, I could fish Penns happily for a day using any variety of tactics on all 3 of the above, though some are marginally better at particular things than others, which usually guides my choice for the day.