I have a second generation SE myself and before that one came out I was always looking at a second hand Series 5 or a first generation SE.
I don't think you can go wrong with a Series 5 or higher. Only thing I would add to that is that the first generation SE doesn't seem worth it since the second generation SE
The first generation is basically a worse Series 5 with it having pretty much the same specs but without always on display and without ECG.
Hope this somewhat helps and guys please, please correct me if I say something wrong here. This is very much based on what I know and my own opinion
I applaud how long you stuck with a Core 2 Duo, but it begs me the question. What were you doing what required so little power to be able to use such a old chip, and. Why the massive jump to a 13900K?