I am new to this forum so I hope I am not stepping on any toes by jumping in with a reply, but there are several variables to your question. The longest kill part throws a whole different slant on how is should be answered. First, from a physics perspective, the longer actual barrell (not counting the pseudo brakes on some models), the higher the velocity which contributes somewhat to kills at longer ranges. Also a fixed barrell, (as on the CFX) should be a little more accurate in the long run, although I doubt that most shooters would ever see the difference. More important, is the choice of pellet, quality and power of the scope, and technique/skill of the shooter. As a former competition shooter, it is my experience that a heavier rifle is preferable over a really light rifle. I read that a quality tuneup by a good air gunsmith will make all this easier. If you want to hunt and kill at longer ranges, I say get a .22 over a .177 then add a quality sighting system, and practice/experiment until you can consistently put every shot where you want it at the range you will be experiencing in the field.
