I think you hit the pros. Case life improved accuracy. With my 06' I full length about 1in 4 maybe only 1 in 10 when shooting cast. The way I do my neck sizing is with the die spacer normaly used for seating (washer)38s with a 357 mag bullet seating die. Basicaly you would back of the sizing die from a half to 2 turns. At 2 turns on a 30-06' is only sizing about half the neck and never touches the body or shoulder. On a 308 with its short neck a half turn will still size all of the neck and just touch the body if your rifle has a big chamber.

On the down side odds are good that the neck sized cases won't fit another rifle. I have 3 06's and they won't swap necked cases at all. It gets a little bit hard to close bolt on the 4th load with my full load.

Hope that helps