The increased far clipping plane is one big reason why it runs so bad. When I set r_farz to 8192 my FPS goes from 60 to 200, however it's still not as high as most other maps (a minimum of 400-1000 fps depending on the map, even some of the HRCS maps run this good) and it gives a visible seam which is why you increased it in the first place. Maybe you could add some fake fog in the skybox like what HL2 Update did if you don't mind putting some custom textures in the addon or even just change the fog color to match the bottom half of the skybox.

so epic.

novo