To be honest I have never paid attention to the RPM's beside a simple sanity check. 800 RPM on a 120mm? Hmm.... 2300 RPM max on a 200mm? Hmm...

I pay more attention to the static pressure and flow rate. Unless the fan RPM is listed at 5500 RPM I can be fairly confident of the performance at a reasonable noise level.

AnandTech did a review of 8 radiator fans in 2012:
[URL]http://www.anandtech.com/show/6177/choosing-the-best-120mm-radiator-fan-testing-eight-fans-with-corsairs-h80/5[/URL]

Also keep in mind the difference between CPU/radiator- and casefans.
You want air pressure for pushing air through obstructions (like a radiator) and high air flow for moving a lot of air out of your case (sacrificing a bit on pressure). Of course within a given RPM/noise limit.

Casefans: high air flow, low/medium air pressure
CPU/radiator fans: medium air flow, high air pressure