I have a Ruger Guide Gun in the .375 Ruger. I bought it for a trip to hunt Sitka Blacktail deer on Kodiak Island (I heard there's some bears up there). It is a GREAT gun! Very handy, reliable and tough as hell. I love the gun. I shot a couple Blacktails with it. One at 310 yards, and the other was a 75 yard off hand shot (pictured below).
You already have two .30 calibers rifles. I suggest you consider the .375 Ruger. If not, then I would definitely recommend the .338 Winnie . You can't go wrong with either.
Make sure you wear hearing protection though. It's "painfully" loud!