Well, in my current save I've done over 60 missions across 13 "programs", and still not finished the tree. Science Mode, 60% gains, DMagic and ScanSAT parts offsetting that. I'm playing ironman too, no quickloads or reverts except for bugs, and that's the big one - it means caution with Kerbals and a lot of probe work, as well as repeating the whole mission if something goes wrong. I haven't necessarily tried to just grab science either, I've done several programs where the goal was just to do something else and any science was incidental. As far as tech tree progression goes, well I obviously got solars as soon as possible. I remember leaving the 2.5m engines until late, before then I was putting Reliant+Swivel clusters under my 2.5m tanks and that worked well enough. With DMagic the science parts were spread around the tree more so I couldn't rush science in the same way I would with stock parts. And then when I had a bunch of science I rushed the spaceplane parts because I wanted to make a spaceplane.