Salt - I'm sorry but the term 'knock down power" is mis-leading. (Unless you hit an animal in the head with a sedge hammer.) What you are looking for is a cartridge that delivers enough energy to provide shock to the muscle, circulatory and nervous system. This shock is the energy transferred from the bullet. Your 30-30 has and will continue to kill a lot of deer every year. I know what it is like hunting in PA. We do have a lot of hunters and some areas get pretty jammed up.
I've shot a lot of deer with a 243, 270, 7-08, 308, and 30-06. Most of them shot with the 243 and 270 drop where they stood. The one I shot with my 7-08 never got out of his bed. The only deer that ever went any distance when shot were with the 308 and 30-06 - but usually no more than 50 yds.
The point I am trying to make is that it isn't only the bullet/cartridge that kills quicky. You, as the shooter, have to do your part and put it in the proper place. What I do and told my son and any young shooter is to visualize a basketball setting between the shoulders and aim just below the center of it. This placement will surely take out both lungs and one or two major arteries.
Any cartridge from .243 on up to 30-06 will be adequate.
Good luck with your selection and practice shooting from hunting positions.