Actually, no need to give up on those maps. It's only 2-3 areas where you will experience some performance hit and only if you fly too close toward the city. The rest of the map (99%) will be smooth for you with high FPS.

No. Thats a different way to display distant objects - its used in many games, but its not existant in IL-2. Even the most far LoD is a 3D model. A simple one though.