People will tell you they regularly shoot vermin at 50 plus yards with a 12ft pounds air rifle, and indeed I understand Field Target competition includes a target at that distance, but hitting something and killing it humanely are two very different things. One of the first things an in-the-field Rifleman should learn is that of judging distance and fortunatley the air rifle is probably the best bit of kit for this as trajectories, even at 24 ft pound energy, are rainbow shaped at 50 + yards.
I really only use my air rifle for squirrels these days and if I take one at 30 yards it is the exception. Most are 20 yards or closer. I didnt opt for an FAC rated version to enable longer shots but rather to have the comfort of greater penetration that comes with the power increase. Im afraid even I dont always make a clean head/neck shot, and if the critter moves at the moment of trigger release, an all too regular occurrence given the nature of old flicker tail, that power can mean the difference between a wounded and lost squirrel and one that at least gives the opportunity of a follow-up shot.
I guess this is a long-winded way of suggesting whatever the power in your air rifle, keep the max distance at around 30 yards. Im sure there are thousands of airgunners out there who would disagree though.
Cheers