Up until May of 2008 I mostly hunted with a BAR Safari II in 7mm Rem Mag with 160 grain Sierra Gameking bullets. Never needed anything more for antelope, deer, or elk. However, I wasn't shooting over 400 yards. I give the BAR to my oldest son for graduating from High School. Believe me, it was well worth it.
I did some trade work back in 2002 and had Christensen Arms put me a custom .300 Ultra Mag together. It has a 26" barrel with a VAIS muzzle brake and sits in a MPI thumbhole stock. The scope is a Leupold 6-20x50 Long Range with a custom elevation target turret. I handload with 96.0 grains of RL25, Fed 215M, and 180 grain Nosler Accubonds. My muzzle velocity is 3,400 fps. Personally I've only taken two cow elk with it. One at 491 yards and the other at 608 yards. Both one shot kills. In the fall of 2008 my cousin used this rifle to kill a 368 7x7 bull elk at 973 yards. The 180 Accubond was a little light for that distance but put the bull down with a low spine/high lung shot.
I just finished building my own .338 Ultra Mag using a Rem 700 action and a 28" fluted barrel from Lilja. It sits in a Manners GAT thumbhole stock. With the Leupold Mark 4 6-20x50mm scope it weighs in at 12 lbs even. So far I've worked up a 250 grain Sierra MatchKing load averaging 3075 fps muzzle velocity with clover leaf groups at 100 yards. I'm looking forward to stretching this rifles legs at longer distances in the near future. With 250 grain Accubonds or TSX bullets it should be a killer rifle on elk... as long as I don't have to pack it far.
I think, however, I'll head back to mostly hunting with the 7mm Remington Mag. I recently purchased a Remington Sendero SF II chambered for this cartridge. Performing a few accuracy enhancing modifications should turn it into a decent long range shooter. With Berger producing the 168 grain and 180 grain VLD bullets with ballistic coeficients over .600 the numbers are very impressive out to 1,000 yards, and with allot less recoil. I personally think this is plenty for elk out to 850 or so yards. Each to his own though.
The pic below is of my cousin's bull he took last year with the .300 Ultra Mag.