I'll bite. I don't think Peralta is a true ace. He seems like a great guy, and a good player. 3 is a stretch. He's a very good 2 IMO.
He was great today, but typically he really labors to get through 5 innings. It takes him too many pitches to get guys out. It sounds like cherry picking a flaw, which I suppose it is, but it's what keeps him beneath the upper echelon of guys in my opinion.