I've been using a Marlin 336C in .30-30 for over 25 years and love it. If your longest shots are in the 150 yard range like you said, then I can't see any reason for switching. Over the years, with the possible exception of the .30-06, Marlin .30-30s have probably taken more game than any other caliber. I'd say save the money, you're already set!