I agree with some of the posters here that chop rushing is overpowerd. Take a look at a capital using 2 food resources and 2 mined grasland hills giving it a production of 6 and a good food production for early growth, workers and settlers. I like such a capital as great civilizations always started in food rich areas. Now add 8 forests to this city. They represent 8*30=240 production ripe for the plucking (at normal speed). That's equal to 40 turns of production from the city (if it is improved with mines). You must completely lack any kind of sense for gaming strategy if you can't see that to chop these forests is a great way to improve the strength and expansion rate of your empire. Thus all players who realise this will focus their research on bronze working to chop forests and build a few workers to chop the forests fast. Because it is such a dominant strategy, it is an overpowered strategy. No other strategy is interesting compared to this one. I would reduce the value of forest chops to 10 each. (I have actually already modded that into my own game.) Then the forests around the above mentioned city would represent a production value of 80 or equal to 13.3 turns of production of the city. Still valuable to chop these forests, but not that valuable to make it a dominant strategy. I have also given jungles a 10 production chop value in my game to make a jungle start somewhat less bad. I don't see why (from a realism point of view) forests are more valuable for production than jungles.