I have a .22 Gamo Nitro. 1200fps using Devastator ammo. Okay, have to cock between shots though.
Have you tried different pellets? Heavier pellets would reduce muzzle velocity and increase retained energy. The accuracy is said to increase markedly once the muzzle velocity drops below the speed of sound (about 1100 fps, depends on temp and air pressure).
Gamo has a video on their site that shows a feral hog being taking by one of their air guns.
http://www.gamousa.com/videos.aspx. When I last viewed it, it was the top video on the page.