Sure. But I'm approaching this from the assumption that we're actually talking "observed/resultant performance" and not "baseline required performance," i.e. ta

Sure. But I'm approaching this from the assumption that we're actually talking "observed/resultant performance" and not "baseline required performance," i.e. talking about "'excess' performance over the required threshold," and if that regresses due to a correctness issue, I don't see the problem. Now what is "the minimum required performance threshold," I cannot say, but it is surely at least the ability to render on "CPU" at 60Hz. (which CPU? render what? using how much of the available CPU power? with how many frames of latency allowed?) Note that I don't fundamentally disagree with you and I cringe when I hear issues dismissed as "premature optimizations" myself.