FYI, this was a question in my mind too, the real-world usefulness of a small caliber for PG. I will spare you the research (including a few threads here on AH)
https://www.africahunting.com/threa...-antelopes-opinions-please.45286/#post-478661
To make a long story short, the 257 Wby has been incredibly effective. When I tested it the first time in Africa, I went on a dedicated PG and MG (mountain game) safari in the Eastern Cape, and used it for a long string of one shot kills from Vaal Rhebok to Roan. I experienced 100% one-shot-kill reliability on 17 animals.
https://www.africahunting.com/threa...ill-safaris-even-better-than-last-year.52376/
Now, in truth Roan in Africa, or Elk in the USA, are probably a little past the upper limit for the caliber. Yes, the 100 gr TTSX launched by the .257 Wby kills elks every year in the US, but my personal view is that you must limit yourself to behind-the-shoulder-double lung/heart shots when using a 100 gr .257 slug for this class of animals. But if you do that, the results are absolutely astonishing.
I have owned .222, .223, .22/250, .243, 6 Rem, 6.5x54 MS, .270 Win, 7x64, 7x65R, 7 Rem, .308, .30-06, .300 Win, .300 Wby, .338 Win, .340 Wby, 9.3x62, .375 H&H, .416 Rigby, .458 Win, .458 Lott, .450 #2, .470 NE, Lord, what do I forget? and I can state unambiguously that the .257 Wby is the most versatile caliber I ever used.
No, I will not try it on Buffalo, as Roy did (a stunt if you ask me), and when I go specifically after select trophies in the 500+ lbs. class I bolt on the .300 Wby barrel on the R8, but in truth, I now use the .257 Wby 100 gr TTSX for most of my PG and MG hunting.