A lot of answers that don't much seem aligned with your original question.
If varmints are primary, deer are a distant second, and your state has no restriction on chambering for deer, I think the .223 is just fine. If you want to get "custom", by all means do an AI. But if coyotes and lesser varmints are its main prey, I wouldn't step up above .22 caliber.
Just my dos centavos,
Rex
