I only read through about five pages of this, but I'd pick a Liger (I don't know if that's a common pick). Lion father/tigress mother, experiences hybrid vigor from the parents. I'll just make sure I find a nice, healthy specimen to acquire, as they sometimes have health problems. A healthy, normal weight for a Liger is 1000 pounds; they're HUGE compared to either of their parent species, but just as quick as any big cat. Keep in mind, this is no bigger than several species of prehistoric big cat, such as the American Lion of the Pleistocene period, so we know animals that size lived and hunted as predators.