Iwaki's are great if you don't spend much time in the room that the aquarium is in, or the pump is located in a basement or other room. If not, the fan is just too loud. I just put a Poseidon PS2 on my 120 and It is dead silent. I would not put a 1000gph pump on a 55. I think a Posiedon PS1 would be a great quiet pump for a 50 and with a penductor you would have plenty of flow. If you really want a 1000gph pump you could get the PS4 you would just need 2x 1" drain pipes.