Do you think a .177 caliber pellet rifle firing at 1000 fps is capable or maybe better put adequate for killing small game like a possum cat or rabbit?
Yes, a .177 pellet rifle will kill small game and critters. I've been doing it with 750 fps since 1968 with a Benjamin Model 347 I got for my birthday. Just requires good hits same as any other gun used for the same purpose. Penetration has never been a problem. To this day the mighty Benjamin has been the actual home defense gun around here for it's the one pressed into service for any pesky back yard critters.
This squirrel died happy with the peach in his mouth, taken while sitting in the top of a pecan tree.
The Benjamin was advertised to make 750 fps with 12 pumps in the brochures. After getting a chronograph I tested this. 10 shot average was 752 fps with the Benjamin brand .177 pellets in the green metal cans with the screw-on lids with a 10-shot extreme variation of only 10 fps. Never saw a self-contained metallic cartridge firearm achieve such consistency.
I hunted rabbits with the Benjamin as a teenager, even long after obtaining a .22 rifle. Cottontails never proved very tenacious of life when fairly struck with a pellet traveling 750 fps. 750 fps will drive a pellet through an armadillo's shell to the vitals. They leap into the air then expire. I took out a large raccoon with the Benjamin fairly recently with a head shot from behind the car to where he was crouching underneath next to the inside of the right tire. Sometimes the .177 pellet exits the skull with raccoons, 'possums, feral cats. Nearly always exits with skunks, squirrels and rabbits unless the shot is very long.
I had shoulder surgery back in the fall. Both right before and right afterward the ol' Benjamin was difficult for me to pump, especially rapidly pumping 12 pumps as in an "emergency." Only a couple months back I picked up an RWS Diana Magnum 350 in .177. This one's suppose to deliver 1250 fps Came equipped with a RWS branded 4X scope made in China. Has accounted for one squirrel so far and was undeniably effective. Discharge of the RWS is quieter than that of the ol' Benjamin. We love squirrel and they get turned into squirrel and dumplings . We have both apricots and peaches coming on and the squirrels are already bedeviling the green frunt, but I'm ready for 'em this year.
