The main visible difference between 8 and 10 is the foliage and trees. There is MUCH more flickering (lower quality) foliage and trees when set at 8 than when set at 10. Problem is its hard to get good frame rates when set at 10 if you turn other things up. My settings now are exactly at what Franziscas are set to, I run a 5870.

When you are standing still his observation is correct, you can't tell the difference. But when you are running you can see a big difference in background foliage quality when set to 8 instead of 10. It is not worth the performance hit IMO though.