I know all about the pellet densities but what are some opinions on ideal pellet weights. H13 7 shot seems to weigh around 1.5 gr/pellet. H13 6 shot around 2.2 gr/pellet. H12 6 shot 1.8-2.0 gr/pellet. Anything over 2.2 (H13 #6) grains seems needlessly heavy. I have weighed a lot of H12 #6 and unless you pick out the big pellets it does not weigh more than lead 6.
If those TSS weights are correct (#9 1.2gr) then wouldn't size 7 HS @ 1.3-1.7 gr be more deadly than people may realize. When I reclaim my shot I sort out 4 diff sizes and the smallest I get is probably around 7.5-8.5 avg size and 1.3-1.4 gr per pellet. I save these for 1 oz 20 ga loads for my son. They are around 320-340 per oz.
The optimum pellet is picking a pellet size and material which allows you to get a good quantity of individual pellets per ounce in a shell for a good dense pattern, with shot small enough to achieve good pattern density and low wind resistance, but with enough weight to retain good down range energy, and lastly hard enough heavy enough and low enough drag to fly streight and true and not flair away from the point of aim excessively. Not an easy ratio to work out for maximum effectiveness, and everyone has their own ideas as to what achieves the best mix of attributes. Thankfully there is a wide range of ratios that will achieve good clean kills at acceptable distances. I think many of us are guilty of fretting over this stuff too much.