[Jeff Higgins]

A .22 caliber pellet rifle is no more "powerful" than the same model in .177 caliber. Pellet rifle power is entirely dependent upon the "engine", be it a big spring in a spring-air gun, the reservoir in a pneumatic gun and its "exhaust valve's" ability to open against pressure and fully evacuate that reservoir, etc. Caliber has nothing to do with it, other than bigger bores using the available "engine" a bit more efficiently, but not enough so to really notice.

The .22 will be far better for backyard pest control. The bigger pellet will smack 'em noticeably harder. And, believe it or not, it will probably have less penetration than a .177 in harder targets, like your wood fence, due to its greater frontal area.