I am also taking both for the June session. I am probably as disciplined as you are, we will require a lot of focus as I believe it is a lot of work. P5 pass rates are terrible.
I’m taking them together as my options too, I want to get everything out of the way in June and thought these were the best 2 (the advanced tax book looked massive, and I’ve heard very bad things about P4, so they’re both out!)
I think it’s a good combination, obviously both require you to really put the hours in, good luck.