I'm no Histo expert but a thought to consider. Do you need to build (m)any metros?
You won't go above the 512 limit on just a standard map and avoiding pollution is good for your score. Maybe you'll need some metros once rails increase your food supply but I'd imagine that getting to this point will take quite a while and so maybe you'd be better off getting full use from the tiles you have rather than waiting to be able to build hospitals. Once you have sanitation, you could then flood the remaining tiles to get additional specialists and expand some of your cities into metros. All you would then need is a market to keep everyone happy, which has got to be better than temples, caths et al.
Just a thought...
You won't go above the 512 limit on just a standard map and avoiding pollution is good for your score. Maybe you'll need some metros once rails increase your food supply but I'd imagine that getting to this point will take quite a while and so maybe you'd be better off getting full use from the tiles you have rather than waiting to be able to build hospitals. Once you have sanitation, you could then flood the remaining tiles to get additional specialists and expand some of your cities into metros. All you would then need is a market to keep everyone happy, which has got to be better than temples, caths et al.
Just a thought...