You don't need pass through penetration like most expect/get from TSX's. Do not lump Bergers in with other such as Nosler BTip, which has a lot of first hand documented failures to penetrate past bone to reach the vitals. You only need to penetrate into the vitals, they don't need to come out to kill. If you prefer a blood trail, then my all means go with the all copper TSX. You will trade off the occasional pencil through where no damage is done though.
Bergers have more than enough sample size on elk with very very few reports of them not penetrating enough to turn the vitals into soup. Second hand reports about friends should be considered just that, second hand. If you are on here inferring that these bullets will not be reliable, then please provide your personal experience with them in your post.
If you just don't trust the theory of Berger bullets, don't use them. If you don't have first hand experience, then don't talk like you do. While others may argue, the close tolerances of the way they do the jacket, along with the tip of this bullet the "delayed" expansion theory here seems to work very well.
I do not say the same for other VLD "fragile" type bullets such as the Sierra Match King(SMK) or similar "target" bullets. These bullets have a long and documented track record of fairlures, Berger's don't.
Again, personally I have taken 6 animals with these from my 7mm and have not had any issues with them blowing up AT ALL and that includes 3 elk at ranges out to ~450.
What you are looking at using, 140gr, 3000fps+, 600+bc, that is surely all a 130gr 270 can deliver, even all a 270wsm can deliver, with half the recoil. So I would say it will do the job. Not saying the 338 is overkill, and would pick that first if your only criteria was foot lbs of energy, but if all your asking is will this 6.5 do the job, with Bergers, then I say YES!