I shot a doe in Pa last season just over 400yds according to my girlfriends dads GPS.  She was broadside and standing still.  When the bullet hit her she dropped like a ton of bricks and didnt move a hair.  All the conditions were just right and I was in the prone position.  No wind.  There was no way we could get any closer for that shot and unless I get a perfect opportunity like that again I'll never try it again.  300 yds is my max for the most part and thats with a good rest.  Offhand, no more than 150 or so.  My gun of choice is a Sako 3006 shooting Hornady light magnums w/ a 150gr SST.  +1.5 at 100yds, -6.5 at 300 and -20 at 400.  I dont guess it hurts that I like to shoot alot either