The Sherbourn will power just about anything.

The M80 is a much larger speaker than the CMT-340. If you are looking for loud volumes, the M80 will get louder than the 340.

As for differences to the Polk, I would bet that you would hear them. If they are to your liking, only you will be able to be the judge of that.

I say take the demos, and listen for yourself.