This didn't go how I thought it would go. I did a lot of reading of that thread, videos etc. I set up video to watch myself and didn't like the angles. I think my old setup was pretty relaxed, and the new one was just way too upright. I tried lowering the adjustable stem, and I could get closer to 90deg w the arms by lowering it and stretching out. Ultimately flipped the adjustable stem, probably at about -18 because it's straight forward. I'm about 4cm down from my original, instead of 4cm up. And now about 4cm forward from where I started.

I could have gone lower by dropping the spacers, I tried but that didn't feel good (I wanted to lean on my hands). That lower position actually looked like a 90 deg arm position. But the new one is much closer. I took a 20 mile ride to try it out, upper back felt fine. So maybe what I needed was to stretch out more, not to move up.

Still feels like I'm using different muscles and I have to get used to this position, but the bike didn't feel wrong. I probably need more time to evaluate but I think I'll do it at the lower position, not the higher one.