As far as my tech costs go in my current Japan game on Monarch -
Around 1300 I was 6-7 techs ahead of everyone else and my techs were coming in at about 15-20 turns each. I had 3 cities in Japan, 1 in Korea, 2 in Phillipines, and 1 in Okinawa (Naha). I sold 2-3 (we are talking techs like Calendar, Paper, Guilds) to everyone for some easy cash.
Fast forward to 1600, I'm working on Steam Power, my tech times are about the same, maybe a tad quicker, I've snagged 3 cities in China after their collapse also, and suddenly England has Rifling and everyone else grabs Military Science. Seems like the computer does a good job of catching up in the Renissance (which is pretty accurate). But I wonder if they would've gotten up there so quick if I hadn't helped them. Around 1500 none of the European powers had Astronomy so I helped them out so they could get to colonizing.
I hope all of this helps!