Most rifle length barrels I have used get around 700-720 fps with the various CB's and are plenty quiet enough, quieter than most of my more powerful air rifles as well as leaving them in the dust in regards to power. The Colibris are quite a bit less potent; less than one third the muzzle energy.
I sure wouldn't want to tackle a woodchuck with a Colibri either; I would think the CB would be the bare minimum to ensure a killing headshot. They penetrate fairly well. The Colibris, not so much.
Be careful of your backstop with CB's. At any shallow angle they can and will bounce if you're not paying attention.