I have not taken an elk with a Barnes XLC, but I know guys that have and they say they are awesome. They have used them in Africa and here in Colorado. I have 180gr for my 30-06 and they are accurate as heck otu of my Tikka. They aren't handloads, they are just factory Federal Premium. They are supposed to keep pretty close to 100% of their weight because of the all copper construction and when they pedal out into the "X", they are supposed to spin and cause my damage. I cannot wait to try them out, because I didn't get a chance to last year because of the nice weather...no elk.
That said, my wife's grandfather has shot more deer and elk than he can count and he believes in speed. That is not what the terminal ballistics(TWBA) reports show, they say a bigger hole and deeper one is the key. They also say that hydrostatic damage isn't really a factor because most organs are elastic and can take the temporary wound channel with no problems.I have seen the formulas for a fast, light bullet vs. a slower, bigger bullet and the bigger one has more energy.
That said, he's always used a 270 and/or a 30-06. He likes the smaller, faster bullets. He did say that he tried ballistic tips once, but they blew up on the shoulder 2 times and blew up in the neck on the 3rd shot. He had a Nosler Partition that finally put it down ( he had used them before that and used them since)and he will not change from Nosler, except for the Barnes. The ballistic tips he used were years ago, I'm sure and they're better now.
I still don't know how they'd hold up if they hit something close, though. Or if they happen to hit a twig or something on the way through.
I guess there's just going to be two camps on this, and the main thing is still the placement of the shot. The bigger bullets just tend to give you a little more insurance, I think.
I hit a Mulie doe this past season with a 150gr Remington bronze tip and it didn't quite penetrate all the way through from 175 yds or so. It did stop in the opposite flank after taking out the lungs, though. Dropped her right where she stood and she was long dead by the time we got there. She was a good sized one too with lots of fat for the coming winter.
And a 180gr Barnes XLC does ruin a jackrabbit's day in a hurry!