I think you're massivly overthinking this. Let me answer this as clearly as I can for you buddy (I'm sure I already have in another post of yours) in FAC air everything a .22 can do a .25 can do better, you already have the better calibre slot dont change it.
.25 FAC generally hits harder, carries more energy downrange, resists the wind better, and expands more reliably with slugs, so overall it just delivers more impact and consistency than a .22 a .25 can also be more accurate than .22 at longer ranges because it buffers the wind better keeping those groups tighter.
As you've already mentioned you're looking at some form of variable setup like an FX Impact etc... There is very very very little benefit in chainging to a .22 you're essentially downgrading in my opinion, however you seem quite set on a .22 for reasons I can't quite understand, I could be wrong but I feel like you've been watching too many you tube videos of Matt Dubber & his South African friends going shooting and you've thought.... I want a bit of that (only natural

) if this is the case just remember they all run their FX Rifles in .22 because you can buy them in .22 essentially over the counter license free, when they get to .25 and the energy levels can ramp up they may require a firearms license which is why they generally stick with .22 & they enjoy all the rifles FX send them for FREE, they're all sponsored by them after all.
If you're adamant you want a.22 just put in a variation and wait, let me put it this way for you, I have 2x FX Impacts both in FAC one is in .22 and the other in .25 and the .25 is far far better i will be at some point be putting in a variation to change my .22 to .25.