Updating My Simulation Computer - Need Ideas!

Hello Gang!I have a home-built rig that has served me very well over the last year but it is time to upgrade it. Here is my current specs:Intel Pentium 2.7Ghz Quad Core NVidia 8700GTX 500GB of video RAM4GB of RAMWD Raptor 150GB 10,000 RPMASUS Maximus motherboard with inboard sound8 Cooling fans700W Power supplyWindows Vista 64I am running FSX SP2 and with all the myriad of addons, it is running adequately. I have not been able to overclock my Quad Core to a level where it is stable - if I go above the 2.8 level I start gettng all kinds of issues and have to rever t back. I also suspect that the onboard sound is getting some power out f my processors, so I'm thinking about getting a sound card to handle that chore. Some folks have recommended that I change the MoBo, the processor, and the video card to something more powerful.What do you folks recommend?Thanks for your input!Dennis D. Mullert