Why not just aim for the off shoulder if you still want to hit bone? As for caliber my buddy's 6.5-06 with 140 Sierra SBT's has taken some large bulls over the years and somewhere taken at 500 or 600 yards. So you do not need a monster magnum and that rifle has 4 bulls that score over 350.
I shot a cow elk at 80 yards in the high shoulder with a 7mm STW and a 180 Berger VLD leaving the muzzle at 3150fps and she dropped like a brick. The bullet went through the shoulder and bottom of the spine and exited. Here is a picture of an exit on the off shoulder from a cow elk I shot with the same rifle and load at 357 yards. Granted it did not dead center the shoulder but it did hit some bone and a rib as well.
I watched my brother in law on his first cow elk bust both front shoulders with a 200 SMK out of a 300 win mag at 284 yards. The bullet was found under the hide on the off shoulder. That never knew what hit her. My cousinís first elk was shot with a 190 Berger vld out of a 300 wsm and it was a higher shoulder shot. Again that elk went down hard.
Now if I knew I was going to shoot an elk in the timber and at hard shot angles I would plan for it and choose a bullet like an Accubond or Partition and so on.