In both games im getting a rapid distant mountain flicker, its rather annoying and im just not sure whats causing it. It could be a game issue unrelated to mods as its in both games.

I've not noticed flickering mountains in FO3 (not got NV) but...

I've been suffering from flicker distant textures. The worst offenders are distant billboard poster and the Raider graffitti on walls. It's especially bad when lloking through a scope. I changed some of my nVidia controll panel settings (like enabling tri-linear optimisation, clamping negative lod bias) as recommended on the Tweak Guides site and this has helped a little, tho its still happening.