We may be comparing apples to oranges on this one. If you're going to shoot square to the target, as Creeper mentioned, then the common rules about stock sizing go out the window. The tradition cross-body mount used by hunters and target shooters uses a longer stock that those used by squared-off run-n-gun shooters.
Since run-n-gun is an offensive action, I'm not sure how it relates to HD. You might get more realistic HD practice if you shot from a La-Z-Boy in the dark of the night (none of the ranges around here allow that).
BigJim, my friend, sorry that they're picking on you. Those of us who know you realize, in your neck of the woods, you only need one stock size: One that works with rain gear.