landscapewaterfall01.nif
landscapewaterfall02.nif
landscapewaterfall03.nif
landscapewaterfallfoam01.nif
landscapewaterhoriz01.nif
landscapewaterhoriz02.nif
landscapewaterhoriz03.nif
landscapewatervertbot.nif
landscapewatervertmid.nif
landscapewaterverttop.nif
Several of the ULs, OC Leyawiin Reborn, Elsweyr Anequina, and I'm sure there's others too. Any mod that drops files into meshes\landscape\LOD you should avoid touching those files.
If you install mods with BAIN, all you have to do is give the optimized Vanilla Oblivion meshes a lower priority than other mods that change meshes. I have organized all 450+ packages in my BAIN folder, and I do not have to worry about reinstallation or overwriting things I do not want to. Plus, the conflicts with every installed package is visible at all times. (You can toggle different conflict viewing settings, such as enabling view of inactive package conflicts.)
@Arthmoor: Thank you for the information. I will add and organize it all when I get back in a few hours. What do you recommend for the shadowmapresolution setting? Mine is still at the default setting because I was unaware of such an issue.
Edit: One more thing, are the UL mods' meshes optimized, any of them?