Personally, I'd go ahead and add the second card. You don't HAVE to have it for boxing, it will mean you can improve some settings while boxing, but that's not the main reason I would add it. I would add the second card because it'd be a sin to not put it in there with that monitor. For DOOM or Witcher III, etc, that setup will be a treat to play on, THAT is where you'll see the real benefit of the second card imo. Not saying it won't help boxing, but it's REALLY going to be noticeable when you're playing something from your Steam library.