The 1:28 is a real good sabot shooter. I shoot 100 grains of Triple Se7en and a 300 grain Hornady XTP with outstanding results. It will also shoot some maxiball real well.

The 1:70 is an excellent roundball shooter. And because of the slow twist, you can really put some powder under that ball. I like the big bore, but you seem to have it made with your points.

I would get the 28" barrel unless of course you wanted a stalking rifle or tree rifle, then the 21" would be real good. Although I have never shot one of them.