After trying protein-only in PWO for a while, I went back to almost pure carbs again yesterday, to see if it would make a difference in recover. IMO it made a HUGE difference!
If you do enough reading, you'll see arguments on both sides. But from what I can tell, it's still best to go high carb after a very heavy session, with a bit of protein, then a meal shortly after. It'll keep recovery times short, and let you work harder next time
Or at least it wil help you stay comfortable.
I can also tell me insulin sensitivity is improving.