> they claimed that this offer is in 75th percentile of comparable companies.
Empirical data is the best data: https://angel.co/salaries
Bummed OP had the original offer rescinded, but for anyone reading this in the future, a quick Google search for "startup salary survey" should bring up a few additional resources. I've filled a number of these out in the past and the data is always awesome. Lots of 'em are behind paywalls though, so beware.