I reinstalled everything and the latest version of all the plugins i used instead of Rebirth, gave a try to Remiros grass for a change (previously was using Ozzy Merged Grass).
Setup MGE XE , generated the distant lands and all its required mesh/static generation too.
Started Morrowind and wow, it's incredible how the performance is high and smooth despite all the superb dynamic shadows , the long view distance, the water reflections etc... What a performance difference with OpenMW in which every of those features had sadly a very noticable impact on performance, i really wonder why it is like that out of the lack of lods of OpenMW, is MGE XE doing some magic somewhere

Not fan of remiros' grass at least in the starting area, i prefered the ozzy merged one.
EDIT :
So much difference in performance seemed a bit curious to me, so to check if by any chances i had a setting from the very old version of OpenMW i tried somehow breaking everything in that latest dev build, i simply deleted the OpenMW folder from C:\Users\YourUserName\Documents\My Games\
Restarted latest dev build of OpenMW and set the settings.
Even applied the required openmw.cfg and settings.cfg (files that are in the recreated C:\Users\YourUserName\Documents\My Games\OpenMW\ ) changes to have my remiros grass appearing in OpenMW :
https://modding-openmw.com/mods/remiros-groundcover/ Started the game and ... performance was much much better, still not as amazing as what i have with MGE XE, but in comparison to my previous test, it's like night and day. I wonder what setting was screwing up everything previously.
Then after more tweaking, OpenMW now refuse to launch with some unicode error , even after deleting the folder in my documents or the openmw directory still same error now. All the while Morrowind still works without a single problem.
So it looks like it will take time for me to move to OpenMW as currently Morrowind + MGE XE is running rock solid and like a dream on a now low end system
