Boxing over Kickboxing in a street fight? Im not sure about that and yes i know you said IMO. A kickboxer would win faster( well maybe not faster) and in a more devestating way simply because of more weapons in his arsenal rather that just hands.
I used to think the same, until I read got fight. If you throw a kick in a street fight, you're off balance and there's a good chance you'll get taken down. It's going to be eye gouging and crotch kicks from there. I would think moving forward and boxing would be your best bet since most "street fighters" couldn't throw a proper kick to save their lives.
Traditional kickboxing does not involve elbows, but since muy thai has become so popular, many people combine both. Having practiced both extensively, I can tell you kickboxing will give you a more well rounded workout due to the full range of movements, but boxing will do wonders for your cardio and conditioning. Both are however excellent exercises to get in shape with.