Ironically I was just thinking the same thing about spacing last night while I was reading on my Kindle. I typically use a line-height of 1.2 or 1.3em in my EPUBs. I wish that Sony had as much user control over fonts as the Kindle does on the device rather than having to mess with your EPUBs. The Kindle has variable line spacing with 3 settings. I wonder which one you were comparing to, Pie? At medium it does seems a little larger than my typical settings. The large is really large. The small is a little small for me. i tend to read at medium on my Kindle.
I know what you mean about the screens. However, when I compare my 950 & K3 side-by-side, it seems to me that the K3 screen is glossier. Also fingerprints seem to show a little more on the Sony screen than the K3.