I'm actually about to put two althons under two dangerden blocks. I have them set up in series. If the performance is really bad or something. I might try reworking it to parallel. I have an Ehiem 1250 pump. I am not sure of it's exactly pressure rating, but it's a fairly large pump and move a lot of water. here is a pic of my series setup. Don't mind those super long wires from the NMB power supply.... grrrr
I am figuring that the pump moves the water fast enough as to make much of difference in the temp from one block to the other... I hope I'm right, as I would like to get these chips up to 1.5Ghz or so.