The area of a 10" circle is a little over 78
sq.in. So, 80 pellets spread evenly should be about one pellet per
sq.in. This is considered as the absolute minimum number of pellets to sufficiently cover the target and expect a kill. Anywhere from 120-150 and it's a done deal.
Your gun may shoot a better pattern with #6s in the 655 and may be lights out in the new Win LB #6 or even #5 load but you just have to shoot and see.
At 30 yards even if you are getting 150 or more pellets it is imperative that you try it at 40 just to see how it varies in just 10 yards. A particular load and choke may shoot high and another could be low and left for instance so you need to know. Whatever distance that you can get these numbers to shine for you should dictate the distance for your particular setup.