Again, that's still the biggest mistake you made. Pulling numbers entirely out of thin air & memory here, so the specifics may be wrong, but the general theory holds. I'll assume an average of 4 commerce per tile, and from memory uni & library are +50% science, cope's & newton's +100%. Size 12 with those 4 generates 52 base commerce, +300% bonus, giving you 208 science per turn at 100%, 104 science and 26 base cash at 50/50 sci/tax. Size 21 with lib, uni, cope's and shake's gives you 88 base commerce, +200% bonus, giving you 264 science at 100%, 132 science + 44 base cash. That's approx 25% more science, 70% more cash, and also 70% more shields, resulting in builds completing 40% faster. So a 20 turn wonder will now take only 12 turns. Plus the possible added bonus of specialists. It's also 8cpt to 6. And you can still go for Newton's, and probably research Economics so you still have the 3cpt backup of smith's. So why not try and build them in the 20k city? Great wall can still help you to 20k, it will probably be good for a minimum of 500 culture. I'm still curious about your tech position. Were you tech leader throughout the MA/IA? Or trailing behind the whole way? If you were leading, then the tech rate will slow dramatically if you simply direct your research better, fast to get good wonders, slow it down elsewhere. If you were behind, 1600 for space is amazingly quick.