Use a heavy premium bullet and you should be OK. I don't know where your gonna hunt but shots can be long. A mil-dot/Ballistic plex/B & C plex scope is helpful. Don't do the math to see where your bullet will impact. You actually have to shoot it at 2 and 300 yards. Keep in mind that weather and elevation will change point of impact. (Air is less dense and usually less humid at higher elev) I say all of this because you really need to be able to "thread the needle" with the shot if you go in under caliber. I have seen elk fall to 260 and even a 243, however they would not be my choice. I usually use a 300 Wby but this year I'm taking a 358 Norma. My first elk hunt I went with a friend that took a 25-06. I was not impressed with the performance and it took a shot from my 300 Wby to anchor the animal. After the elk was down his 3rd shot from the 25-05 hit the spine and finished it. He was using a 120gr premium bullet. I would start w/ a 140 in the 6.5, if your barrel will stabilize a 160 use it. Round nose bullets have tremendous killing power. If a 140 is all that it will stabilize use an "X", Fail Safe, North Fork, Partition...
Just my 2 cents ( looks more like I wrote enough for 50 cents worth)
