I currently run a Falcon FN12, at about 20lb/ft. This is very effective on rabbits, pigeons, rats, etc., out to about 65-70 yards, providing you are on target Most rifles running at 12lb/ft will consistantly kill, (cleanly), rabbits out to about 45 yards, maybe 50 if your lucky, but shooting should not be about luck especially rifle shooting, it should be about skill because the "lucky" hunter will wound alot more of his/her quarry then a skilled shooter. It is best to keep air rifle ranges to a maximum range of 35 yards to be sure of killing cleanly. If you cannot consistantly get 10 shots into a 2" circle at 30 yards you should not be trying to shoot game at that distance. Air rifle shooting is all about field craft. The art of rifle shooting is to get as close to your quarry as possible without being detected.
Practise makes perfect, so a good dose of target shooting every week will enable you to take good clean kills out in the field.
Good luck
Dave