2008 CL semifinal against Barca, 2008 CL final against Chelsea and 2012 CL semifinal against Bayern comes to mind - it's many years ago I'd give you that
In terms of pure conversion rate is there many better than him, but in the biggest moment does he seems to keep his cool the last 5-10 years
Everyone has the technique to score those penalties, yet you see terrible penalties time after time. It's all mental and when you're taking those pens when score being 4-0 to make it 5-0, it ain't nothing. You could almost laugh while taking it and even laugh if missing.
I wouldn't give too much weight on converstion rate. It's lazy way for current generation to see, who has the highest %. Stats are the best way to tell who's the best for the people who ain't watching the games. Like with tennis, even i wouldn't like to admit Djokovic being the GOAT, i'd take him playing for my life all those 4 Slams in year. In this situation, i'd definitely take Ronaldo to take the penalty if my life was on the life, regardless of the conversion rate. That's how i know, deep down inside that he's the best at taking them. I'v seen him nailing them couple inches of the goalpost so many crucial situations, where the whole world wants him to fail, but never really did.