I've been wondering lately... With all the various carb sizes available, how do you guys determine what size to use? I've heard of people going from a stock 14:12 to a 15, to a 19, or a 20 or 21. Why, when you could get a 19, would anyone "upgrade" to a 15? Or why even use a 19 at all, when there's a 20? Or why not just go straight to a 21? Seems like using those smaller carbs is an unnecessary middle step, and not really much of an upgrade... or am I missing something?