You are trying to UV unwrap a level?
I get mental blocks just thinking about that!
I would
NOT UV unwrap a level, considering that it would be nearly impossible to see what is what, and even more impossible to load the 10k by 10k texture.
Here is a simple solution - use multiple textures.
Use tiled textures like bricks, windows, or whatever your game level might need.
For things like rocks, I would use them as separate models.
If you can't use multiple textures in your modeling program, delete it now, and get Blender.
Blender 2.44 (New version!) easily wins over 3ds Max or Maya.
Blender 2.43+ even has mesh sculpting and multires.
Edit: Read your signature, you use already use blender.
Who will die first?