First of all, as a bow hunter (Elk only) and a rifle hunter (elk and deer) I can tell you that the broadhead kills I've done make a larger, longer wound channel than any rifle bullet I've used (including 45-70). The most extreme I have seen was an arrow, by a 14 yr old kid, penetrate over 3 feet of Elk diagonally (long tracking job).
Second, when the cartridge is paired with the appropriate weight rifle, and the shooter has lots of ammo, they shoot up to a 30-06 plenty well. What I have noticed is that the trend towards absurdly light rifles has created some hard-kicking setups. And guys who believe Elk are armor-plated buy rifles chambered for expensive cartridges - and they don't get in the shooting time.
I don't think "wound channel" is the right term to describe the effect of a high velocity explosive bullet. More like "area of destruction". Stuff gets torn up and if the heart doesn't stop immediately you get a very bloody mess (which can confuse the post-mortem examination). On an Elk, IMO, you need your "area of destruction" to be at least 12" long minimum on a broadside shot. On a deer maybe half that. If you can't get the explosive effect far enough into the cavity, then you need a bullet with a large enough diameter to penetrate all the way through important stuff. Most 30 cal fodder will expand 1.5 diameters, (my 45-70 expands to .9" and penetrates 30" of Elk).
I've never killed a game animal with my 223. The only truly explosive cartridge I used on deer is the 270 Winchester, 130gr handloads chrono'd at exactly 3000 fps. The "area of destruction" with cup & core bullets was longer than a small mule deer is wide (fist-size exit wound broadside, legs blown completely off, etc.) Effective killer, but I really had to be careful not to shoot near anything I wanted to eat. Most all my shots were under 150yds.
Lots of track record with the 223 taking deer, so I wouldn't have any qualms about using my 223 in the future. But I haven't seen anything on Elk - and the thought is unsettling.
More opinion, but either a large diameter bullet that crushes a hole all the way through, or a high-velocity bullet that creates a zone of destruction in the vitals.
This is just my opinion. Only trying to help - not trying to step on anyone's toes.