Yesterday was way too cold, and for whatever reason, I just couldn't warm myself up most of the day, despite an extra warm sweater and raising the heat. That said, I didn't go out to get more sandpaper, I didn't sand the crowns, or cut the back mitres.
But all that got done today.
I ended up only sanding the crowns with 80 grit paper. This removed 90% of all the saw marks, and smoothed the round portion quite nicely. They could be sanded more, to FULLY remove all the saw marks, but I'm pretty sure that they won't show up under the 4 coats of paint that will cover them (white shellac sealer, primer, 2 coats of white). And even if they do, they'll be 3 feet above eye level.
I'm very happy with how they turned out.
Side note: They don't look very long because of the angle, but they're 10 feet each (120").
If you look closely at the coved profile, you can see some of the faint diagonal cut lines I'm talking about. It would be a lot of extra effort to remove them completely, without much payoff.
So now that those are done and ready to install, I started to rip out the old "replacement mouldings" which are just a 3/4" quarter-round (eye rolling). And I also have a few drywall corner seams to redo before they can go up, but I'm excited!