Actually, I don't think Swords to Plowshares is that bad in this case. Due to the difficulty, you can stomp the AI pretty bad. When you do declare war, you should be able to take out the capital (and possibly the whole civ if it's their only city) in just 2-3 turns so most of the time you are still getting the growth bonus. What was your strategy for getting Education so early? Did you sidetrack for any other techs (such as Construction)? Did you get lucky with your ancient ruins? Or something else?