After playing around with Aztec in an OCC game, I would have to say that this UB is pretty great. There is no issue with population growth. The main problems I am having, however, are money and resource availability. With regard to money, you can sell off all of your luxuries, etc., but eventually you will lose trading partners to war. Until you can get the gold buildings up and running money is very tight for emergency troop buying or CS bribing. You can potentially raise money by pillaging, but that brings me to problem 2 - resource availability. If you don't have iron or horses (or preferably both) within your city radius you are dead meat on Emperor or above. You can possibly get these resources from CS alliances (if you have the gold to buy them off), but if they are conquered by another civ you are in trouble. So there is a lot of luck involved with initial city placement in OCC. The planets still haven't all aligned for me yet to be able to do this on Emperor or higher.