Re: First time Long Range Rifle
The Sierra 100 grain 6.5mm HPFB is specifically designed for varmints. It can be driven very fast and is flat over 400 yards. It has far less wind drift than anything you shoot vamints with in 223 or 243/6mm. I used a 30/06 w/ 125grain SpFB in the past on varmints so I could become proficient with a single rifle.
Your friend is undecided and not engaged in a rational search. He just wants the flavor of the week. 6.5 mm cartridges would be fine for what he wants. 243/6mm is pretty small for elk and unsuitable for elk at long range.
A better choice would be something for the middle of his intended game, like a 6.5 mm, and make it work up and down the game-size scale than to pick something for the small stuff and hope to push itup to the size required for LR elk. This is a fools errand. Better to pick something for the top of the scale, long range elk size game, and load it all the way down.
The 30/06 is a fine choice but for me the 6.5-285 Norma or 7mm RemMag would be much better. The 6.5-284 is rocking the shooting world right now and that's because it does what your friend wants. He needs a chill pill and a bagel.
Just my opinion.....