Soldato
Just a question though, to enter a new era, do you have to research every technology in that era?
No you don't. If you wanted to "beeline" along a path of the lowest research times possible to get to the next era, and not bother researching anything else, that would be fine. Although you might find that you are a little imbalanced, techwise, if you do it to an "extreme".
For example in the ancient era you can research writing and then start to build the great library whilst researching something else to ensure that when you pop the great library you can use its gift of a free tech to slingshot yourself into the medieval era way ahead of the other AI's. You can even delay the construction of the GL if you need to whilst you are beelining your "fast research" to the medieval era to ensure that the free tech gives you that access, if that makes sense.! It all depends on the level you are playing and what your goals of victory are as to how and what you research.