51.0.
I'm using MO2. Once you choose Delete that mod and its whole subfolder vanish completely into the Trash Bin. Delete is the only way I manage new mod versions unless it's a small 'hotfix' patch that contains only a few files. My F4SE and all plugins, Buffout, etc are in the main game folders of course (never have MO2 manage them). Currently only using SS2 for its building assets, haven't even placed down the first plot from Jake. The long saves are intermittent, not every time, sometimes I get a quick save, other times sometimes so long I have to force quit. That's what happened after the new version - one quick normal save, walked out of the settlement, long save time till I force quit after 5 minutes.