Re: Neck tension-- how much ???
Start 3thou - 1.5thou sprgbck, for ~1.5thou tension on ~.280" worth of neck.
I think you'll find this is sufficient bullet grip, while providing consistent seating pressures and resulting seating depths.
You might even give 2thou under a try, as the lowest tension you can get away with produces the lowest tension variance. But that don't guarantee lowest ES(there are more factors there).
For your load you might need high tension. This you experiment to by varying the depth from .280 to maybe .300(+), or .250(-) for less tension.
And then, it can be a double edge sword in that running high tension, invokes annealing more often, or tension variance will grow to the point of diminished returns(climbing ES, opening groups).
I suspect this is more of a tuning aid for those who are not jammed.