Though not so much an issue among DGS regulars, shooters tend to match shell and chamber length - consciously or otherwise. Frankly, I have more use for the faster Hi-Phez in heavier 2 3/4" 12s. Used it in the 391, a 101, and a M-12 at towers. It worked just fine, to understate by more than a little.
As for the 16 in #5, nothing I ran through my .021 SR M-12 clobbered phez at distance so well. When I took guests out that was my backup gun/load.
I put in a lifetime supply of both loads many years ago. No need for more....unless someone will build me a pyramid.
OK, I suppose a few cases in my burial ship would add some ballast, but that's my final