I've tried searching Google and StackExchange for this one, but I find it difficult to state the problem generally and therefore have had no luck so far; apologies if the answer is already out there somewhere (and easily to be found given the right formulation).
Now to flesh out the rather abstract phrasing in the title of my question - which of the following (if any) is correct:
(a) The performance of Y and Z is comparable.
(b) The performances of Y and Z are comparable.
My intuition is that both are at least commonly used, and perhaps even correct. But do you know of any grammar book that addresses the issue? And what is your intuition as a native speaker (if applicable)? Please don't argue by saying that (b) is more logical, language as a rule doesn't have to be logical :) I'm interested in a normative body's opinion and/or your native speaker's intuition. (If I were a native speaker myself, I'd use whichever would feel most natural to me, not being overly fond of prescriptive grammar, but I don't have that choice.) Thank you!