I'm REALLY happy with a 69.8 inch gear (45x17) which enables me to (as mrbertfixy said) to change speeds easily. Remember, your topend speed is ONLY useful a TINY fraction of the time if you're using your bike on the street (at least on any street I've ever been on). I find that I spin out twice on my way to work, which is fine with me, because the rest of the route, the gearing is perfect to get past all the traffic, out accelerate the cars at traffic lights so I'm not competeing with them for space, etc,etc,etc. Also, when you can accelerate better, you can stomp it when you see that you've placed yourself someplace you should not have (i.e. in front of a car while you're running a red).