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Test 2) Thicker bp Cascade (essentially a copper Cascade SS without jet mods) => Overall CPU temperatures slightly higher and overclock stability was about the same at higher flow rates. Better overclock stability and better temperatures at lower flow rates than regular Cascade. Hypothesis: thicker bp provides a better "smoothing" effect.
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Cather, at the risk of stating the bleedin' obvious. The "smoothing" effect of a given volume of copper must be related to it's heat capacity. Coppers heat capacity is less than that of water but not by a huge amount when stated relative to volume (4.2ish vs 3.5ish J/cm^3.°K).
That said, water IS better, by 15-20% so the more water in the vicinity the better the dampening must be. i.e. the thinner the baseplate the better. The dirty big fly in the ointment is the TIM-BP-H2O thermal resistance, which might nullify any benefit, leading to, thicker BP must be better,
above a certain thickness.What that thickness is I don't know, it might be near zero. A direct die cascade would be interesting. ie no cup bases, the base of the "cup" being the surface of the CPU die.
What I am say is that I am concerned that all the tests showing that direct die cooling gives higher temperatures may be missing the point. The, lets call it "Maximum Attainable Stable Frequency/°C", might in fact be higher, thanks to the high specific heat capacity of water, even though the actual cpu temp could be higher. What the WW and than Cascade showed for me was that mass of copper (or silver) is not important for maintaining good temperatures. What is important is the way the water is delivered to the hot area. Deliver it in the same way direct to die and I can not see how it could be worse.
I am not a direct die advocate, actually I've thought it inferior because of the necessarily smaller surface area, but with impingement in the equation and your observations of overclock stability, I am beginning to wonder.
Cheers
Incoherent