Hey AC_Hacker - sorry for the delay in replying, I didn't get an email notification for your post.
I didn't measure the temperatures before and after insulating, but it's noticeable by feel. I just bought rolls of faced fiberglass insulation, cut them into ~6ft batts for easier handling, and stuffed them paper up into the joist cavities. Afterwards, the floor was noticeably warmer, and I was actually able to reduce supply temperature a little bit.
My system has a fixed supply temperature (right around 98F) from a standard gas tank heater, and the Pi controller only turns the pump on and off after doing temp measurements and prediction of future temperatures and lag of the system, which works pretty well. It measures temps every 60 seconds, calculates heat loss, measures how long it takes for temps to change when the pump is switched, and predicts fairly accurately how long ahead of time it needs to switch the pump to keep the temp at target.
I've got the code for it on github, so if you're interested, take a look (
https://github.com/opiesche/Prometheus). It should work with any Pi, although I've only tested it on a model B, with the Raspbian distro from the Raspberry Pi foundation.
Happy building! This was one of the most rewarding projects I've done - it's a lot of work, but it's certainly worth it in the end!