I have 120g total volume and I think the RS250 is just right, not overkill. Mind you, I have 140lb liverocks and a tonne of corals. My previous RS135 wasn't keeping up, and I hardly feed my fish. I've had the skimmer running for a month now and I must say it's was a very benificial upgrade. Mine has the new black needlewheel and the Gen-x6000 pump. Noise level compared to the sedra 5000 is about double, it humms and vibrates quite loud, definately unbarable if you're in the same room. As well the sucking noise from the venturi hose is also noisy. This was expected with the increase of a more powerful pump, I don't have a problem with it as my sump is in a dedicated fish room. IMO, if your sump is not in an enclose cabinet or room, the noise will drive you crazy.

i have that CS 250 with dual 5000's and mine is quiet all you hear is the sucking if the fine air.

Sedra5000 are not noisy, you can hardly hear the air suction and there isn't much vibration. The Gen-x6000 on the other hand, appears to be similar in size, but is a potent skimmer pump. It's has 3 times the gph throughput of the sedra5000.

I've got two RS 250s. Both are good. GenX 6000s on each. Quiet. Airlines are noisy, but I've gotten used to them. One of them is in the same room I sleep in.

Cheers,