Re: burris or nikon?
I have both Burris models and much prefer the more expensive Black Diamond - better turrets and great glass. 30mm will give you more adjustment range in any scope. Also use the Nikons a lot and have had excellent service when I needed it.
The new Nikon tacticals are very good long range scopes, lots of adjustment range and very good optics and turrets. Very tough choice, Nikon tactical vs Burris Black Diamond but I would go with the Nikon mainly because it has better turrets.
Only thing I don't like about the Burris is the fact that their turrets are smaller and just not as solid and robust as the other guys. If they had turrets on them like the Nightforce or Nikon, or even the MK4 Leupold they would be kickbutt.
My Burris scopes have had a lot of use and they are standing up well. The Nikons are a newer entry but they are also standing up to a lot of shooting, well over 5000 rounds in the last year.
Both offer modified mildot reticles, Nikon even offers a free MIlDOT MASTER with their scope.