I've been interested in big game cats for quite some time, and, in doing research for owning a large predatory cat one day, I came across a breed called savannahs. They're actually a crossbreed, typically a serval (an african hunting cat weighing in at 30-40 pounds) and a housecat. How they do THAT, I don't know. But, the crossbred savannahs are typically about three times the size of a housecat, and about 25 pounds, for the males. And, they're about as gentle as a typical housecat (albeit a great big one). Check out
this site for more info, and
pictures.