like you have any room to talk chris

yes, i have run sicce 3 and sicce 5 pumps externally on closed loops. they are quiet, but if you hard plumb them and that pluming touches any solid part of your stand or wall, a humming noises will result. that may be true of any pump, though. i dont know anything about the sicce 10, that sounds like a beast.

as you mentioned, i have a dart running the closed loop on my 250, and wouldnt consider any other pump on a big tank. it pushes a little more than you are looking for, but it is very close to silent. of the three tanks running in my living room, the loudest noise is the small fan on the lights of the two biocubes.