The main argument against "performant" isn't linguistic, it's technical. "Performant" is vague. It can always be replaced by something more descriptive like "fast", "uses little memory", "asymptotically optimal", "parallelizable", and so on.
Thank you. In light of the fact that George Orwell's "Politics and the English Language" essay was just recently posted here, I want to acknowledge that you make a better case than I do. One should aim to make one's meaning plain, as opposed to resorting to inflated (and often vague) language.