The regular Panasonic fans are super quiet. When I turn mine on there is no motor noise- all that can be heard is a bit of air movement. One thing to think about is that you are paying to heat your house, and the vent fan is also sucking the heat out of your house. There is really nothing to be gained be over-sizing.
I would work hard to avoid the routing that you are suggesting. The ideal vent routing is straight up and out through the roof. If you have a standard shingle roof, it would be a quick and easy job to install and flash a vent outlet on the roof.