Holy cow!
I now have a mod list that includes FCOM, Better Imperial City, Open Cities Reborn for all the rest, RAEVWD, Immersive Interiors, All Natural, all the ULs, Sneaking Detection Recalibrated, plus 3 gigs of texture, normal map, and LOD replacers.
No stutter (and no Stutter Remover) at all, loading times are negligent, and 5-15 actors in combat with no lag.
Added bonuses include much much faster Wrye Bash Installers tab actions.
I'm flabbergasted.
And I recommend upgrading to all who can. Who knew that after all these years of struggle, new hardware would do such wonders?