I just finished reading an interesting study. The study tired to measure flow output of some popular propeller pumps. I hope you will enjoy it as much as I do. Here it is:
http://www.advancedaquarist.com/2011...aign=clickthru
A couple notes:
1. The study was done mainly by an ecotech intern and funded by ecotech.
2. Tunze apparently acknowledges the large discrepancy between advertised numbers and measured numbers and is working on a fix. Go to RC tunze forum for more details.