I had basically the same problem..My specs are below. I reccomend a better video card. But you can try below to see if it helps...
Then boy did I get lucky.
Went over to
http://www.avsim.com/ and downloaded their Cloud Fix v.3. You can find it in the library section.
Now I am running at 120 mile view distance, draw at 60 miles, 100% clouds & Density at High !
Also I have the AI traffic set at 100 % (Strongly rec Project AI at
http://www.projectai.com/ ) Really shocked me shen I saw all the planes on the ground !
And lastly I still can get 20fps at LAX !
WOWGive them a try and backup before, just in-case you do not like it....