The terracota can be unbelievable value as you transition from classical to medieval - when it often ends up being still available. Keep some units unupgraded and do it with
warrior + sword + spear + pike + chariot + horsemen + knight + archer + composite + crossbow
It's such a hotly contested wonder by the AI players, I've never had a game where I can build or upgrade a pikeman and still get a chance to build the wonder afterwards.