There was a discussion about this a while back on the old OC.com forums. In the end they pretty much proved that the water can't go through the radiator too fast. If the water is flowing just as fast through the water-block then it's not picking up as much heat per unit of water, but it's still picking up the same amount of heat, if not more... so even though any given amount of water will not lose the same amount of heat in a radiator it is traveling faster through, there isn't as much heat per unit to lose in the first place (I'm not an expert on this, it's just what I remember).
What I do know is that I saw someone test a TBird peltier setup with different pumps from 150Gph up to 700Gph. 150 was way too low (water became heat-saturate in the block) and was about useless. At no point, however, did a pump do worse than a slower one. The 700 was the best, but just barely bette than the 500 (there wasn't enough heat to justify that much water flow).
Basicly , if you CAN have water going too fast in a computer then the pump you would need to do so would not be of practical use due to noise and line pressure. As far as the original issue, I'm not saying you're wrong, but I know some physics professors that would disagree with you. There are a lot of variables that could account for something like that, but we won't really know without a decent testing method.
-=mac=-