Neither CPU speed nor the amount of memory matter much when it comes to the 3D graphics applications!
The only important component is the video card. Search the Net for video card comparison and see how your card stacks up against those, which run R/C simulators well.
I have nVidia 6800 card and is kicks! Running AFPD at 1900x1400 resolution (the maximum my monitor supports) with all the deatiails and smoothest frame rates.

Boris