Need Advice On Upgrading For Fs9

Hello,My current system is as follow : AMD X2-4000+ ( 2,1 GHz); 2 Go RAM; ATI Radeon HD3850-256 Mo. I am running FS9 on a 22 inch display (1680x1050).I am very happy (over 20 FPS) with it except when flying complex aircraft add-ons (i.e. PMDG 747 or the super nice VRS F18) into complex airport (the new LFPG by aerosoft or FS dreamteam KORD) in overcast condition. (i also use active sky, ultimate terrain and fly from the VC)I consider upgrading the CPU to the X2-6400 (3,2 GHz) but need advice on the graphic card is there any chance it is also limiting ?thanksJulien