The MCP350 is a very good pump; you haven't given us your setup but I doubt the MCP350 can't handle it and it's also very quiet.
The MCP650 is noisy. Undervolting it will decrease performance; you don't want to do that.
The new MCP655 on the other hand, is relatively quiet. About as quiet as an Eheim 1250 according to Cathar. It's even got a speed dial so you can decrease performance and noise if you want.
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