Adrian Hare has a video showing how to pattern and he uses a 20 gauge. He found by trying several different brands from Winchester, Remignton and Federal that one of them just shot better - gave a better pattern than the others. He was suing both 4 and 5 shot.

I suggest you do the same. Pattern each at 30 yards and then count the pellet holes in this target.

http://mdc.mo.gov/nathis/birds/turkey/target.htm

JW