I run two 8800 GTX in SLI. I get the flickering water reflections in water=3, that's it. All others seems fine.

After reading this thread, I tested different Non-SLI/SLI Antialiasing Settings and SLI Performance Modes in Il2 1946 looking for the best visual quality consistent with good framerates. Framerates were measured with "The Black Death.ntrk" and FRAPS; visual quality was eyeballed in both "The Black Death" and some single-player missions.

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CPU: Intel QX6800 (2.93 MHz)
Motherbaord: NForce 680i SLI
Graphics Cards: 2 NVidia 8800GTX (OC'ed to 594MHz Core, 1404MHz Shaders, 900MHz
Memory)
Graphics Card Memory: 768MB DDR3 x 2
RAM: 2GB PC8500
Monitor: 4:3 19" 2ms LCD @ 1280x1024 Resolution
OS: WinXP Pro

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IL-2 1946 v4.09b
March 13, 2008 .dlls

In-Game Resolution Setting: 1280x900 32 Bit

Conf.Ini Open GL Settings:

[Render_OpenGL]
TexQual=3
TexMipFilter=3
TexCompress=0
TexFlags.UseDither=1
TexFlags.UseAlpha=0
TexFlags.UseIndex=0
TexFlags.PolygonStipple=1
TexFlags.UseClampedSprites=0
TexFlags.DrawLandByTriangles=1
TexFlags.UseVertexArrays=1
TexFlags.DisableAPIExtensions=0
TexFlags.ARBMultitextureExt=1
TexFlags.TexEnvCombineExt=1
TexFlags.SecondaryColorExt=1
TexFlags.VertexArrayExt=1
TexFlags.ClipHintExt=0
TexFlags.UsePaletteExt=0
TexFlags.TexAnisotropicExt=1
TexFlags.TexCompressARBExt=1
TexFlags.TexEnvCombine4NV=1
TexFlags.TexEnvCombineDot3=1
TexFlags.DepthClampNV=1
TexFlags.SeparateSpecular=1
TexFlags.TextureShaderNV=1

HardwareShaders=1

Shadows=2
Specular=2
SpecularLight=2
DiffuseLight=2
DynamicalLights=1
MeshDetail=2
VisibilityDistance=3

Sky=2
Forest=2
LandShading=3
LandDetails=2

LandGeom=3
TexLarge=1
TexLandQual=3
TexLandLarge=1

VideoSetupId=17
Water=4
Effects=2
ForceShaders1x=0
PolygonOffsetFactor=-0.15
PolygonOffsetUnits=-3.0

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NVidia Forceware v.169.21 Control Panel Quality Settings (excluding SLI Settings)

Anisotropic Filtering: 16x
Antialiasing Gamma Correction: Use Global Setting (On)
Antialiasing - Mode: Override Any Application Setting
Antialiasing - Setting: VARIABLE
Antialiasing - Transparency: Use Global Settting (Off)
Conformant Texture Clamps: Use Global Setting (Use Hardware)
Error Reporting: Use Global Setting (Off)
Extension Limit: Use Global Setting (Off)
Force Mipmaps: Trilinear
Multi-Display/Mixed GPU Acceleration: Single-Display Performance Mode
SLI PerFormance Mode: VARIABLE
Stereo - Diplay Mode: Use Global Setting
Texture Filtering - Anisotropic Sample
Optimization: Automatically Disabled
Texture Filering - Negative LOD Bias: Use Global Setting (Allow)
Texture Filtering - Quality: High Quality
Texture Filtering - Trilinear
Optimization: Automatically Disabled
Triple Buffering: On
Texture Filtering - Anisotropic Mip
Filter Optimization: Automatically Set To Off
Vertical Sync: Force On

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NVidia Forceware v.169.21 Control Panel SLI Settings (Note: SLI Antialiasing and Dual GPU SLI Rendering Modes are mutually exclusive options; you can choose one or the other but not both):

1. Antialiasing Setting: 4x (Non-SLI)
SLI Performance Mode: Single GPU (NVidia Recommendation)
Benchmark: Frames: 8867 - Time: 162737ms - Avg: 54.487 - Min: 22 - Max: 64

2. Antialiasing Setting: 8xQ (Non-SLI)
SLI Performance Mode: Single GPU (NVidia Recommendation)
Benchmark: Frames: 8808 - Time: 163178ms - Avg: 53.978 - Min: 22 - Max: 64

3. Antialiasing Setting: SLI8x
SLI Performance Mode: Single GPU (NVidia Recommendation)
Benchmark: Frames: 8586 - Time: 163772ms - Avg: 52.427 - Min: 22 - Max: 63
COMMENT: Very, very slight visual improvement over 4x & 8xQ (Non-SLI); not noticeably inferior to SLI16x.

4. Antialiasing Setting: SLI16x
SLI Performance Mode: Single GPU (NVidia Recommendation)
Benchmark: Frames: 7589 - Time: 162316ms - Avg: 46.754 - Min: 20 - Max: 63

5. Antialiasing Setting: 4x (Non-SLI)
SLI Performance Mode: Dual GPUs - Force Split Frame Rendering
Benchmark: Frames: 8904 - Time: 162574ms - Avg: 54.769 - Min: 23 - Max: 64

6. Antialiasing Setting: 4x (Non-SLI)
SLI Performance Mode: Dual GPUs - Force Alternate Frame Rendering 1
Benchark: Frames: 8917 - Time: 162827ms - Avg: 54.764 - Min: 22 - Max: 65
COMMENT: Some H20 reflections flicker unacceptably.

7. Antialiasing Setting: 4x (Non-SLI)
SLI Performance Mode: Dual GPUs - Force Alternate Frame Rendering 2
Benchmark: Frames: 8943 - Time: 163377ms - Avg: 54.738 - Min: 22 - Max: 65
COMMENT: Some H20 reflections flicker unacceptably.

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CONCLUSIONS:

At a monitor resolution of 1280x1024, with otherwise max'ed out in-game and NVidia Control Panel quality settings, most SLI antialiasing and frame rendering settings make little diference in IL2's framerates. (However, SLI16x antialiasing causes an 8fps drop.)

SLI8x antialiasing looks a little better to me than non-SLI 4x and 8xQ antialiasing settings (especially in cockpit views).

Using SLI Perfromance Mode/dual GPUs to force Split Frame Rendering yields good framerates and visual quality -- but not appreciably better than a using a single GPU coupled with 8xSLI or 4x/8xQ non-SLI antialiasing.

Using SLI Perfromance Mode/dual GPUs to force either Alternate Frame Rendering 1 or Alternate Frame Rendering 2 causes unacceptable flickering.

Using the same in-game conf.ini settings but my old, single-card Contol Panel settings of 8x anisotropic filtering, 4x antialiasing, force mipmaps - trilinear, texture quality - high quality, triple buffering off, and force vsync off, my "Black Death" framerate was, predictably, 73fps (vsync off) with more "jaggies" degrading visual quality (8x instead of 16x anisotropic filtering).

At higher monitor resolutions, an SLI setup *may* improve visual quality while preserving playable framerates. It would be interesting to compare these results with 22"-24" monitor resolutions.

Vista 32bit users try this....

With ATI Crossfire, use one Crossfore bridge only... that being the Crossfire bridge closest to the output end of the cards and reboot. The BIOS may or may not redetect, depending on mobo. (on my DX38BT it did)

Go to MSconfig/ Boot and then click the Advanced button and at the top of the screen that pops up, there are two checkboxes... one for Boot Number of Processors (tick this and select the number of processors you have) and the other is Boot RAM Amount... (tick this also and select the total amount of RAM you have), then reboot.

This may or may not help il2 but it does help with regard to the system in general

Obviously to have Il2 running in Vista... Folder Permissions had already been set to Full