I was tired of the faster than historical tech times, so I slightly increased tech costs until I got the game to progress at a little closer to historical pacing.
I don't remember the exact percentages, but I think the increases I used were +2% for ancient techs, +4% for rennaisance techs, +6% for Industrial techs, and +6% for modern techs. The average date for Liberalism went from about 1250 AD to 1450 AD, and the average time for global circumnavigation went from around 1300 AD to 1480 AD - 1500 AD. The computer usually got a space victory sometime during the 1900's. I think around 1950 was the average.
I am not fond of the solution of using a flat rate adjustment to science because the tech process during the early game is slow enough as it is. Having to wait longer just to build improvements would be a real pain.
I'll upload my tech file later today. (I don't have access to my Civ4 computer right now.)