I think it depends quite a bit on things like angle and speed. I'm sure that if it came in behind Earth, in a similar orbit, at an angle it'd be very different

I think it depends quite a bit on things like angle and speed. I'm sure that if it came in behind Earth, in a similar orbit, at an angle it'd be very different from a head on 90 degree angle collision with it headed in the opposite direction. Size alone is probably not a great factor to estimate damage. A starting point, but not final word.