Strangly my DDC pump seems to now be working fine and has been for about a week. I think there must have been some air trapped in the impeller housing which stopped it starting properly.. though might be another reson (thats the reson laing give for the problem, for all pumps with a serial number higher than the one they stated).
As for the D4/5, I would have to agree with DG, "As I commented on DD board, "whats the point of big pump if you need to turn it down?""
If I were building a 3rd system, I would most likley go with a c-systems or for cheapness a hydorl20 depending on the system.
I've got good reson to turn my D4 down though - I dont need 9l/m
When I upgrade, I can turn the pump up to counter the extra restriction, however:
Ive talked about the relevance of flow rates and temperature with a few engineers and from also looking at the procooling test results. We think flow rate above a certian point (3l/m?) will only effect performance by a few degrees - which wouldnt noticably affect an overclock unless it was already on the border of being limited by heat.
As for D4 niose, the pitch is very different to a fan, very high pitched and quite annoying.
At 6v its still there (about the minuim voltage without using PWM to drive it), but much quieter. If you had a silent pc, you would still notice the high pitch a lot and it would be very annoying.
I think for my d4, the differnece between 6v and 12v might be as little as 2-5°c oI would prefer less niose.