I wouldn't exactly agree with Xeb's last post entirely, but there's some truth to it I can't deny.
The fact is is that Wing Chun is not the "KO art" you're asking for. Basically, boxing is going to be the art that will teach you how to deliver the most raw concussive force with your hands. Developing power in Chinese martial arts requires years and years of practice, or to butcher the art by brute forcing through the techniques.
If you want to take Wing Chun, then by all means study it. It's still a solid art with a lot of good technique to it, and can teach you a lot. But it just isn't the most sport applicable thing around, and like I said, it's not the "BOOM, KO" style you were asking for.
So, yeah. I would say boxing. I'd also say Muay Thai or kickboxing - not sure what part of those sports Xeb thinks you'd have a problem with, I can't imagine. (Explain, Xeb?)
PS. I can understand kind of not wanting to do what everyone else is doing (which is at least what I thought you meant by 'traditional'), but if you're looking to learn how to fight quickly and acquire that KO power, you do what you have to do.
Well I started in boxing. Did so for 7 years before I went to college and started kickboxing. And well.. im 5'9" and ive become very flexible over the years. But if you're 5'11"-6' tall I still cant kick you in the face. So one of my biggest weapons as a kickboxer becomes void. Move that around and make me 5'5" now I can't kick guys 5'7" and taller... see what I mean. its not entirely practical to be rolling leg kicks, and body kicks (other than groin kicks) in a real fight.