Thing is I never have any performance issues I have6 gig of ram this scene never uses more than 2.5 gig and I think 1.5 gig is windows! Never a hitch when navigating the scene the radeon 4870 sees that it is smooth as. And processor usage whilst building the scene never goes above 20% so its not like I am using hardly any resources at all... until the render happens. I find it strange that changing these apparantly unrelated settings I can disable atmosphere features , but this is the case... I bet I am the only one lol