OK, so if you start 3000BC, you can't catch up in tech quick enough even if you found Hinduism and Buddhism, while if you start after 1000BC, all of the major religions will have been founded and you can't build good wonders in time, and barb spawns will eat you alive. It seems that 2000BC is the ideal spawning time because 1. You get a lot more techs than you would otherwise be able to research and you will still be able to found some religions 2. Lots more units means more huts 3. With your initial units you can usually capture 1-2 early civs starting positions which will buoy your tech up quickly. It might help to give random promotions to starting units for the much later civs (e.g. after 1400 AD) because it's just impossible otherwise to conquer some cities.