I have checked a few barrels of Gamos with a hole gauge and they are the same size, it's where the pellet is inserted is different between rifle models, some are honed out to a larger diameter that other models..
Genesis rifle I would have to give it an 7, weak barrel lock up, barrel pivot bolt came loose on me 3 or 4 times before I fixed it so it stays put. It's a good shooter, and the stock is real comfortable
to grip, the scope is fair since I got a new one from them, the first one would go blurry every time you shot it, but they sent a replacment within two weeks. I have heard that most of the problems with the Genesis have been fixed by the factory.
I don't know if the .20 barrel would go on a CFX and what problems that would come across, I'll look into it some more.