I have killed 6 of them, all spot and stalk with the closest shot being 300 yards. Two with a 243. 1 with a 6mm CM. One with a 270wsm, and 2 with a 6.5 prc. My preference is the 6mm.
Between myself and new hunters I've taken out we have used the 260 Rem, 6.5x55, 264 WM 270 Win, 7mm RM, 30-06, 308 Norma, 303 British, 358 Win, 35 Whelen and 375 Ruger. They all worked.
I liked the 270 Win with 160 gr Partitions best, penetrates at any angle and opens a good wound channel. Going to try that bullet in my 6.8 Western since it works so well. The smaller 6.5's did well too. I carry the 35 Whelen when going out with young hunters in case they make a bad shot. Cleaned up a couple of messes with it and things end fast when needed.