In case you missed the edits in my previous posting:
Boris i know you wanted everything to lowest settings possible.
But my first test with ReduceSystemMemoryUsage=false was stable even at maximum settings and >150 mods and every effect on.
Running it without perf mon i also was able to alt tab in and out. I always had to alt tab 2 times on skyrim to activate it again. this time it was also possible by alt tabbing 2 times. this is in fullscreen mode in skyirm_prefs.ini and
[WINDOW]
ForceBorderless=false
ForceBorderlessFullscreen=false
in enblocal.ini
I wandered from town to town enter some inns and went out again. No problems!
Of course ugridstoload is set to 5, because every other setting is unstable not because of memory usage its because of papyrus scripts not developed for more active cells!
Edit:
this is from an inn in one town, walking to another towns inn: