8x60 would seem to be to much gun just for a 16 to 20 lb animal, if that was all you were going to hunt. Especially for a full body mount. Might do a bit more hide damage than you would like.

I used a 218 Mashburn Bee on my Steenbok and it was plenty gun. I just made sure I had 45 gr. soft points and not varmint bullets.