I am about to replace my old WH 77 with a precharged gun.
What I don't like about the spring gun is; the noise, that fact that I can't get it to shoot consistently(scope issue).
What I do like about it is that it gives nearly 1000fps and around 42joules/ 31ft/lb. I have shot small game up to nutria(not so small) with it and never had problems with power being an issue. Accuracy sometimes, yes. Power no.

So just how fast/much energy is sufficient in an air rifle to make it fun to shoot without having to worry about too drop inside the 30 yards and power on things like larger birds and small mammals?
This gun will be used mostly for shooting rats (outdoor, longer ranges, up to 30m)

Inside 30yards 12ft lbs kills everything very dead with head shots that you would shoot with an air rifle. 25 ft lbs in a 20cal is impressive indeed.