Martin, unless you can keep the coolant at a CONSTANT temperature, testing with more/less pumps skews things. I tried this, with the RD-30 at 18v and then at 24v. All I got was higher readings at 24v due to the additional heat dump... you know that pumps dump less heat the more loaded down they are (more restriction). So naturally, without a chiller to keep the coolant at a constant more restrictive blocks will have an unfair advantage right off the bat. The only way to fly is with a chiller and a way to vary flowrate. Swiftech has such a setup.
And RRR for you to say that testers are biased if the MFGR gives the tester a block is just asinine. With that said, there is not one test or tester out there that you approve of. Sometimes you should learn to keep your mouth shut.