The "on-line" myth seems to be that accuracy is a function of bullet weight (at least in 223 or 5.56 world). I have barrels that shoot 55 grain FMJ very well (under 1 MOA) and I have used them successfully out to 600 yards (Steel with Flashers). My ballistic chart indicates that I'm pushing the super-sonic envelope at this range... but (obviously) the bullet is still moving.
If I have a special shooting challenge where a heavier bullet might offer an advantage... heavy targets, 20 MPH winds, spinners, etc., then I might go to a heavier projectile. But if I just have to hit a target... I'll go with the lower cost option that gets the job done.