Now, with all your kind help, I made some tests and found my settings for a smooth horizon, an almost realistic sky and faster FPS. In case somebody is interested to know these settings I made a few images for you.Thanks again for your help.

the problem ive found with enforcing vis limits, is when flying at night, the horizon is totally cut off much lower than it should be and you can see stars twinkling way below the horizon. oh well, I guess until FSX, it wont be perfect