With Australia + Machu Pichu you can raise your adjacency bonus for commercial hubs to 10 if you have a tile with river and surrounded by 5 mountains (theoreticaly even 11 if you are completely surounded by mountains). Further with "Free Inquiry" + "Town Charters" you end up with 20 Gold + 20 Science just for one tile without any building!! The hardest problem for higher difficulties will be to obtain Machu Picchu faster than the AI.