I'm not the best, but I have hit people at the dojo who are better trained then me, higher ranked then me, more experienced then me, with a headkick. They expected it, they were trained to block it, actually they can argue they were an expert at blocking them, but I still managed to kick them in the head. If I can slip it past them, I can slip it past someone which probability tells me doesnt know how to react (let alone block) a kick. Chances are hes never seen a kick go to his face (i mean, its an alien concept for a non martial artists to see, let alone experience since kicking someone in the head isnt an easy thing to do) or seen a human leg (that can out-match the speed of a untrained persons best jab) be propelled at a high speed to his face.
But, I wouldnt go for a high kick, which is strange when people ask me about the streets and kicking, since I am a high kicker. Its just not needed, I have jeans on and tim boots. A low roundhouse kick would drop an unconditioned leg in a second, its quick and dirty, and an even odder concept than blocking a head kick for an average person is blocking a kick aimed at your thigh. Now... go back to where it says I wear boots, and you know where I am getting at where its just reasonable for me to do this instead.