In 80% of my games, is too big technological progress in XIX-XX century. Radio in 1820 AD, United Nations in 1850 AD, tanks and bombers in 1870 AD, computers in 1900 AD? No problem, mostly for AI (on monarch difficulty). I think this is little non realistic. In my opinion, costs of industrial & modern era technologies should be increased by 75 or even 100% (for any players of course).
In my last start with USA I did a little correction in XML files in 1772 AD, by setting the research percent (on marathon gamespeed) from 350 at 900. Effects?
Industrialism - 1890 AD
Flight - 1895 AD
Radio - 1900 AD
Mass Media - 1920 AD
Plastics - 1930 AD
Now it is 1936 AD, and there is no yet on world such technologies like:
- Advanced flight
- Rocketry
- Computers
- Fission
This is a correct technological progress in my opinion.