The FAC power thing is something I've thought a lot about over the years. My thinking now is that .177 sub 12 offers enough of a flat trajectory to negate the use of FAC air (for me) as my shots are all taken within ranges that will kill cleanly at sub 12 in .177
I think if I ever were to go FAC now, it would probably be .17 HMR. Again, I dont need the knockdown power of .22RF