Hm i'm only using a 8800GTS with 640MB and i have no issues with the latest WHQL.
I don't use nhancer and i have set AA and AF to app controlled in the driver and activated in FSX.
And i use no magical "tweaks", i only try to reduce the memory load as far as possible (reduced textures...90% of the add-ons are using "wrong" texture formats and can be easily reduced with no loss of visual quality). Maybe that helps someone.
Trashing FSX with "HD" textures (HD clouds, HD water, HD Trees, HD runways etc + tons of AI traffic + a large LOD radius) will certainly lead into a blurry mess and stuttering.
For the last shots, i used the AI Formation tool (SimOuthouse). That's why they have their lights on
Thanks! Also for the Infos!