It's interesting to contrast "Measure. Don't tune for speed until you've measured" with Jeff Dean's "Latency Numbers Every Programmer Should Know" [0].

Dean is saying (implicitly) that you can estimate performance, and therefore you can design for speed a priori - without measuring, and, indeed, before there is anything to measure.

I suspect that both authors would agree that there's a happy medium: you absolutely can and should use your knowledge to design for speed, but given an implementation of a reasonable design, you need measurement to "tune" or improve incrementally.

0: https://gist.github.com/jboner/2841832

I mean...you should always design with speed in mind (In that Jeff Dean sense :) but what 'premature optimization' is referring to, is more like localized speed optimizations/hacks. Don't do those until a) you know you'll need it and b) you know where it will help.