I'm seeing two questions: CZ 600 yea/nay, and 20" ballistics for the 30-06
I don't really have a useful opinion on either, but for the second part I would recommend providing some specific information about your preferred .30 bullet weight/type, handloads or factory ammo, shooting distances, intended game, etc.
I'm inclined to think that a large capacity case like the '06 would be more efficiently mated to a longer barrel, but it may not really matter depending on your circumstances.
Also, how firmly wedded are you to the '06?
I've not handled a 600 yet, and I've no idea about action smoothness. There is a current recall in place for early rifles, so it looks like they missed a bug or two.