Oh, and if GPP are so important, is it maybe worth picking up the Parthenon? I was building it for the failgold, but I'm 8 turns from accidentally finishing it and none of the AIs even have Aesthetics yet. Even on NTT maps, alphabet does come in handy for keeping an eye on where everyone is tech-wise.
Parthenon is not bad just a bit underwhelming, and usually (though not here) if we don't prioritize it the AI will build it fast on high difficulty. The reason it's underwhelming is that percentages are mostly additive not multiplicative, so if your Civ is in a golden age with pacifism it produces 3 times as many GPP (200% bonus) and Parthenon would bring that to 3.5 times (250% bonus). I think that's why sampsa said it was worth less since he's generating all his great people in such a golden age + Paci situation.
Also you have to make sure to build it in a city that won't produce great people to avoid accidentally getting an artist.