Well if the difference between two blocks is only 1°C at full load - i don't think anyone would care. All other factors become more relevant, as price, mounting mechanism etc..
And i believe this is the case for most current 'top-dog' waterblocks - TC-4 and so on. Why buying one over another ? Not for the extra 0.5°C you're supposed to get if you mount it perfectly along with the appropriate pump and a fantastic rad.
I care more about being able to clean the waterblock innards, to mount / dismount it easily, to check for corrosion visually, and not to pay too much for it.
So testing, yeah, but to define roughly a group of 'able' waterblocks, vs a group of 'not able' waterblocks - where the expected difference is more than 5°C or 10°C. More precise than this, is not insteresting for the buyer. It is for the manufacturer, to improve and optimize his designs. But mfgers should have testing benches, CFD sims and so on... Or at least they should delegate that work to Bill
