Jack O' Connor's favorite caliber was the .270 win, and from what I have read the 7 x 57mm mauser was a close second, with the .30-06 a close third. The 7 x 57 has a great history of performance. Nice choice. If I was in the market for a 7mm I would closely look at it or the 7mm-08 which ballistically is almost the same. Just because it is old doesn't mean that it doesn't work anymore...
Shot placement is number one in my book, as long as you have a reasonable caliber for the intended game.
no magnums for me.....ever.