Well, I don't, and probably never will. The way the tech is buffer now I don't think it's possible (for me at least) to complete the tech tree. Even with a massive researching network and 100% funding right now some tech (like Phasor 4, Terranforming ...etc...) already take me like 25 turns to complete, and I have seen 30 turns tech down the line.
+ In an easy - average game: the type of game that I can afford to Shift the budget 100% to research time to time along the game and can still keep up with the Military race, then in these game I probably defeat the AI even before I finish 2/3 of the tree.
+ In a hard - hardcore game: now I don't play these games yet, but consider the difference between Normal and Tough, I think if I play an intelligence game I ain't gonna have much oportunity to fully funding the the research and keep up on the other aspect of the AIs. This can make a longer game but probably with a slower tech advance.
Don't seem to work either way to me

. And it's not me though, I saw people posted on other forum that they never reach the end of the tech tree either. Anyone thing the buffer need to be scale down a little bit?