I have the 1250 pump, its seems very powerful and does a good job. I just got the water cooling system up and running last night and is still doing the leak test right now. But the hum from the pump may end up bothering me. Its not terribly loud, but my water box will be up on my desk. I have the pump mounted on rubber grommets on the floor of the water box, so not sure of any other way to mount it to quiet it down. I guess my question is, is the D5 as just as powerful or more powerful as the 1250 and quieter? If so how much quieter would you say? If I end up replacing the 1250, I need a pump that is powerful enough for a dual 120mm heatercore, cpu (tdx )and 2 maze 4's. (no sli atm, but in the future).