I made the switch to a Diablo DC5500 from a Sicce Syncra 4.0 about 2-months ago and I'm very impressed. While the Sicce was pretty quiet after it broke in, the Diablo has been dead silent from day one. I like the soft-start and control for doing water changes. I can dial back the flow and do a 10-15% w/c now without having to completely turn off the pump, whereas before I could only pull 5% or so before the sump ran too dry. The controlability is nice for those with full siphon overflows. I have mine splitting between two systems that total around 150g of water and it's dialed back. Plenty of power.