pH - I think you misunderstood what I said. I agree with you about the velocity thing. But velocity in one point of any loop is constant. On other words, velocity through a 1 inch segment of a hose will be constant (minus bends, etc). To increase the velocity, you can pinch the line. Velocity will increase through that area while overall flow will decrease. BUT you can't pinch a waterblock. Thus, making smaller channels would increase the velocity, but lower the surface area. That's all I was saying. That there is a sweet spot there as well. And yes, I agree with you in that an increase in flow rate will never hurt waterblock performance, and usually help (until the point of diminishing returns). The converse of that statement holds true with radiators so in that sense, there is a sweet spot. um... basically what you said
-Kev