1. Longrifle is certainly correct.

2. The term "knockdown power" is hottly debated. Bullets do not literally "knockdown" game animals. They do/can instantly incapacite them.

If you've got a gun that's in 270 or are looking at one you shouldn't feel the need for a bigger bullet on deer. (The 270 is just a 30-06 that shoots a slightly smaller diameter bullet.)