Actually, you probably want to do both. The World tab controls the multiplier of how long it takes to research a tech, which allows you to set the pace of tech advancement. However, if you increase the research time you should increase the max turns amount, too or everything just takes the default 40 turns.
Unfortunately in 1.29f the max turns itself has a max limit of 99 in the editor which is about right for a triple cost mod. More slower advancement than that will just hit the max ceiling most of the time until the late game.
I haven't got PTW yet. Did they fix this?
Never figured out why there even has to be a max limit for a max setting... It should be entirely the headache of the mod maker to set a right max value for his mod.
Note also, that if you slow tech advancement you will get a more even tech race as a byproduct because the civs will have more turns to trade techs among themselves.