That's probably exactly right. I had a coach once who told me to use an effort like that as an estimated 90 or95% of true max. From what I know about "zone" training, a few beats in error in estimating zones won't be a big deal. I'd bet that 190-195 as your estimate of true max would be plenty accurate, more accurate than most people (who use the age related formula). That's what I'd do anyway.