The accuracy difference definitely has some overlap. Boat tail designs reduce drag which means better velocity retention at distance. That being said I know a few folks that shoot Rem Corelokt out past 600 meters from a 308.
If it were me, I'd say anything under 300 is "flat base" territory with boat tail territory starting at 200. That 200 to 300 area I'd call "transition" area where either bullet will do just fine.
I don't have any scientific basis for this, just my experience shooting rifles at short and long range.