If you're shooting outside of 400 yards, you don't really have a shot.
You ever wonder why you can land hits on a target out to 800 yards but you never do much damage? Because bullets lose a lot of impact power the further down range they fly. Dispersion also has a major effect. It might take you 800 rounds and 100+ hits on a target at 800 yards before you bring it down. At 250 yards it would take 100 rounds and maybe 30 hits to do the same.
Set your convergence for the range you KILL at. Not the range you think you want to hit at. Doesn't matter if you spray at cons at 800 yards, so you set guns to that hoping for long range kills. What matters is once you're done tickling the bugger, and he breaks into you, or another con engages you, and after a fight you get a kill shot, what range is that?
99% of the time it will be under 400 yards, so setting your guns out further just screws you over when it comes time to get the job done, and done quickly.