I've read a couple of remarks recently on various calibre related arguments about the importance of 'energy transfer' and shooting through quarry. In high velocity powder burners the velocity of the bullet can cause huge cavitation injuries which will increase the wound damage and thus hasten the demise of the quarry. Furthermore, hydrostatic shock can further cause damage some distance from the wound. But is this likely to be the case for relatively low velocity airgun pellets? I don't think so for the simple reason I can find no hard evidence to suggest it's so (although there are plenty of opinions supporting every available option or alternative).
If I'm right, then 'energy transfer' is a meaningless concept. By contrast, there are plenty of videos of people receiving shots to the ballistic armour they are wearing from rounds such as 7.62 NATO without even being put off balance. Likewise, shots to large dead animals suspended on a rope show very little movement. On this basis what kills quarry with sub 12 ft/lb air rifles is tissue damage, bleed out, and nervous shock. Such is my opinion. If I'm right, then the only real difference between airgun calibres is the amount of tissue damage they do on their way through the quarry's anatomy, which difference is going to be marginal at best, I would suggest.