Well thanks for all you have done, i couldn't play the games without ENB anymore.
By the way, i seem to have fixed the terrain rendering issues for Fallout 3 and NV with and Without ENB.
Normal mapping and vertex color rendering finally looks like it should.
I was fixing rocks up, making proper UV's for them and made a super high res rock texture and stumbled into a seemingly nasty problem.
The game uses texturesets, all texturesets that can be found in the esm are probably rendered in a single pass, but there are also meshes that refer to texturesets that are not there in the esm file, so i assumed (from my experience with Unity) that these texturesets the rocks refer to in the nif files are created at runtime, and logic suggests that these texturesets on rock would be rendered in a different pass, this would probably mean that all lights and shadows have to be rendered again to hurting performance, but that aside, i disabled all references in the nif files to these runtime texturesets, and all shading errors are completely gone, normal maps render exceptionally well, even without ENB (vanilla they where hardly noticable, now it looks superb) vertex colors on rocks and terrain are beautiful, there are no blending errors with terrain textures when detailed shadows are enabled, no weird shading issues with terrain quad rendering (which normally happens when adjacent quads doesn't have the same texture as it's neighbour and that texture that one cell doesn't have is being painted at the cell border, what happens in vanilla without ENB, also with ofcourse), and my fps skyrocketed, i no longer have any dips whatsoever, some places in the game (FO3) always had fps issues at certain points no matter how fast your pc is, thatis all completely gone.
I will try and see if it works the same for Fallout New Vegas, but i suspect it will, Fallout 3 is absolutely gorgeous now.
Maybe some things i say aren't entirely correct, but i'm guessing i'm close, i'm not a technical as you, so you might have a better idea as to what exactly is going on.