So what are you classifying as varmints? PDs, Groundhogs Coyotes What? Hit a PD or Groundhog in the belly with most anything and it's going to POP varmint bullet or not.
When I first started PD shooting in SD I used a 22-250 and a 308 . The 22-250 was awesome out to 5-600 yds for splat factor but a 125 NBT in 308 was much better beyond that range.