This has gotten interesting - but we're pretty far off from the original topic of How does the ultimate waterblock look like?!
I'm wondering if it makes sense to move a lot of this conversation into a new thread.
My own personal bias would be to call it something like "Living on the edge of semi-adequate cooling for the sale of low noise - silent PC watercooling considerations" - oh wait - that'd run off most everyone's screen
- but you get the idea.
As a "for instance", I run 120mm Panaflo L1A fans. They start out OK noise-wise and get pretty quiet once I undervolt 'em to 5V
If you go to Panasonic FBA12G performance curves
you can see that the rated performance of the FBA12G12L1A (the fan I'm talking about) is at 13.8V - so at 12V it's already undervolted
Anyway, if you look at the curves for this fan, the 7V performance is less than half the 13.8V performance - so it's a pretty good bet that 5V performance (even though it's "off the chart") is less than 5/14th the rated performance.
So... 13.8V rating is 68.9CFM and 3.30mmH2O - and I know I've got less than 5/14th of that or 24CFM and 1.18mmH2O (.046inH2O)
So now, when I go to Radiator Heat Dissipation Testing
The author (Bill Adams) says "...reasonable low and high speed/thick bodied axial fan applications (0.015 and 0.05 in. H2O) resulting typically in 75% or so of “rated” output
..." (emphasis mine), so, hmmm reduce my WAG by 25% to 18CFM and .0345inH2O.
The amazing thing (to me) here is that I'm not "off the bottom of the scale" - which is what I expected when I started this exercise in guesswork.
Could be I did something obviously wrong, though (feel free to correct me...)