I currently have a "Cowboy" and have owned a GG. I sold the GG and bought the CB for Cowboy shooting and because I liked the longer sight radius. That being said, I have seen a lot of guide guns with scopes and being used as deer and bear guns. Both work for the purpose but the CB does not lend itself to mounting a scope. It was meant to be shot with iron sights and/or a tang sight. I am sure you can mount a scope but the guide gun is a better choice for that.
I have not had the rifles chronographed side by side. However, my guess is that the longer barrel will produce an extra 100fps+ depending on the powder used. If you are shooting BP loads, the barrel length won't make any difference.
