In my constant struggle to get FSX working well, I had always messed with the scenery and weather tabs to try and increase performance without sacrificing too much quality. As I have had little luck with that, I decided today to try the general graphics settings. I set up the CS 757-200 with a  detailed McPhat livery at Newark Liberty International Airport (NEWR) and set weather to "Gray and Rainy". I tried lowering resolution, but that gave me little to no FPS increase and a major quality hit (though lower resolution coupled with DX10 worked reasonably well). While no filtering gives a performance boost, everything looks grainy, and I don't see much of a difference between the different filtering methods, so I just left it at bilinear. Then I decided to try something I hadn't before: turn off anti-aliasing. You can see my results at the bottom.

With AA turned off, my frame rates improved a good amount, going from 12-16 to 20+ (I have my frame limit set to 20, so I don't know how much of an increase there would actually be, but probably 2 or 3 FPS more). But, as you can see from the picture, edges are a bit jagged (obviously, as that's what AA corrects). Now, I don't think that they're too jagged, and it's certainly preferable to poor FPS, but I did find a way to get rid of at least some of the jaggedness. Go into your video card settings and find the Anti-Aliasing settings (for me, it's under Gaming>3D  Application Settings) and set AA to a lower setting (I have mine at 2x). Now your video card is controlling the anti-aliasing and not FSX. I hope it works!

Now, maybe a bunch of other people have noticed this and I'm just making a fool of myself posting this, but it works well, so I thought I'd post it here just to be safe.  ;)

http://img26.imageshack.us/img26/9765/antialiasingtest.jpg

Uploaded with Imageshack.us

As you have an ATI card have you thought of using the shader 3 mod as that might help you get back some of your performance when you have lots of cloud cover.

http://forum.avsim.net/topic/283701-bojotes-shader-30-mod-for-fsx/

Its a 30 page thread so make sure you read it so you can see its development over time and see if there is any issues you might encounter.

if i had an ATI then the chances are i would use the shader 3 mod. Also are you using fsx or the ati contral panel to set AA within the sim ?

Remember though that the shader 3 mod can be unstable for some and if you install it you can no longer use the FS Water Configurator app.

I use an ATi card and I have always been advised to keep the ATi control centre settings to "Application based" and use in game changes. I have tried card settings and the results end up blurry. NVidia cards are advised to change on the card settings.

Shader 3 did not work for me, and of course I didn't like that it turns overhead view into a light blue mess. Turning off AA gives me good enough frame rates, so I don't think I need it anyway (though clouds still are affecting my performance).

are you using any addon cloud package like rex as HD clouds can have a very heavy effect on fps.

Nope. Lately I've been trying out different reduced-sized cloud textures. I just downloaded some DXT3 clouds, and I'll see if that works. I've been using these cloud textures called Oscar Clouds which have given me a few extra FPS.