Is there a reason you guys didn't just add something like an extra 10 techs or so that were between techs 2 and 3?
Rebalancing being annoying I take it.
Military Tech increased unit effectiveness on a mostly linear scale. Economic tech unlocked new buildings. Cultural tech improved relations effects and country management. Buildings usually increased tax or levies by a absolute amount, with universities and monasteries increasing tech spread by percentages. Pretty simple system if you ask me.
Did this work differently for Pagans and Muslims?
Edit: For perspective. increases in tech in EUIV, can lead to geometric improvements in performance of one's Economy, Navy, or Military. It is a much deeper system IMHO, as the player is constantly forced to make decisions on how to most effectively spend their MPs, and to a lesser extent, ducats.
EU4 system is far more linear as you have only three research fields.
CK2 has two categories, each with 6 sub-groups (all in all, 18 research groups with 8 levels). Since ToG expansion, you accumulate MIL, DIP and CUL research points (increase depending on Monarch skills, Councillor skills, events and battles also ad MIL points) and have to choose which sub-group to level-up. Additionally, cost of level-up depends on neighboring provinces (as each province has its own tech progression), ahead penalty, your spy studying technology in foreign states and event modifiers. There is more strategy involved in CK2 research than EU4 research (which is now practically a simplified version of CK2 system).
As for cultural differences, certain cultures have different start (Norse for example have advanced naval tech and Muslims are generally more advanced) and since SoA Sunni Muslims can choose a school of theology which greatly increases growth of research points. There is not much difference between cultures per-se, but different cultural units and economical position means you may have to choose different groups to focus on leveling depending on playthrough (also, will you ignore certain research sub-groups and accumulate points to level up some other sub-group).