RE: ultramags help a hunter out!
If 400 yards is going to be your maximum range then you would be much better served with the standard or short magnums. The UM's do not have any real world advantage over the standard magnums under 400 yards. They are made to deliver substantial ammounts of energy at great diatances.
As far as your accuracy is concerned the farther you are willing to strech your yardage the tighter groups you would want to have. Shooting at 400 yards I would want at least 1.5 MOA and would strive for under 1 MOA.