Landscape painting vs imported landscape (static meshes) performance differences?

i have been thinking about this, the landscape tool does seem a little bit overkill for what i had in mind and your suggested skybox terrain does seem better suited since most of the terrain would serve as an unreachable background but my map would be bigger than the average counter strike or tf2 map (i think as i did not play tf2 and cs has been a lifetime ago) and i do not know where the cutoff size wise for static meshes > landscape tool would be when it comes to performance

hope i am not remembering it wrong but in UT3 the onyx coast map was fairly large and i was thinking maybe at most about 1,5x that one but not bigger

yes LODs will be crucial to me from what i remember after reading the documentary for a quick overview of what the engine offers, definitely will have to look into it again