OK, here is my 2 cents.
I've killed lots of stuff, much of it big and tough with various Nosler Partitions. A very reliable, deep penetrating bullet. Very consistant over the years.
On the other hand, the whole Barnes X family has had a somehwhat erratic history. While their TSX bullets appear to have a very good, consistant history for reliability, the bullet in question is not one of those. It's a TTSX. Designed to open at lower impact velocities, etc. It also has a sectional density of only .200. While the light, older X's and even the TSX do surprisingly well when pushed good and fast when it comes to penetration, we aren't talking about one of those here. Just what it will do in an animal at the velocity it is pushed, simply isn't known. Like some have said, it will kill them. Well, so will lots of lessor loads. The question is which is "best."
For my uses, I insist on something that is very reliable and capable, w/o a doubt has lots of penetration on animals like elk. I'm certain I'll get plenty of that with an NP. What I don't know is just how well the new TTSX, especially in that light a bullet will work.
The other thing is that Nosler Partitions retain alot of their weight at lower impact velocities. The 180 gr. Federal NP load in the .308 has a first class reputation on elk class game. Similar, but not quite the same. Still, given the rep of both, I personally would have more faith in the 210 NP.
Now, if it were my .338 Federal, I suspect I'd handload a few 210 TSX's for my hunt. E
