Dave I'm just getting into this as well. I made a homebrew concentricity gauge. Thought I'd relate some of my experience so far. I am only shooting under 200 yards (270 Howa) so we have similiar circumstances.
In my very limited testing, there seems to be less relevance to neck runout than there is to loaded cartridge runout, but you should probably do your own data collecting and testing to verify. The method I ended up using was to write the actual runout measurement on the loaded case (e.g. .00025"). Might seem a bit ridiculous, but, you can then take your loaded cartridges and group them together for the various shot strings you'll eventually take with those rounds. You MIGHT be able to make small predictions in group behavior if you were to shoot those strings and record the shot groups for the purpose of matching those groups to the measured cartridge runout. Make SURE you aren't changing little pieces of your cartridge 'recipe'. For example don't load a string that has a 20 thou jump, and then load a string that has a 60 thou jump. That will make your testing completely irrelevant. Same bullet, same powder, same charge weight, same primer, same case (prep'd the same way), , same shooter, same day....etc. Take your runout measurement on the same location of the bullet for each and every bullet (loaded cartridge).
There will be plenty of posts that say don't worry about it and just load and shoot, and they might be correct, but if you are like myself and few others that I know, you are interested in the rabbit hole stuff just as much as the bang.
