Ok.. I'll clear up what I meant
I meant 1/2ID vs 3/8ID (which with ClearFlex 60 would be 1/2OD).
Now that that's cleared up....
The real question, I guess, is which is better to have:
Water moving faster through the system, which all other things the same, you should get with the smaller tubing.
OR
More volume of water, though at a slower speed, which is what you should get with larger tubing.
And if the answer is "It depends on the complete system" then that's fine.
I would assume that blocks made for high flow systems like the Cascade, PolarFLO, MCW5002 work better with the 1/2ID tubing and that blocks designed for lower flow like the Asetek WaterChiller, Culpex Evo, Zalman WB, etc would work better with 3/8ID tubing.
But that is just the assumption of someone who has been doing water cooling for 6 months now and wants to make sure he knows what he is doing, not just *thinks* he knows