Economic card

Hello,I have a PC with below info which at the time being runs FSX at 3-5 fps with Ultra settings in almost empty airports (DX10).- Pentium Dual Core, E6600 @ 3.06 GHz- 4G DDR3 1033RAM (FSB 1066G)- 1TB WD- On board G41 Express Graphics.Which one of these graphics cards may increase the fps to a higher level?- HD6670- HD6750- GTS450- HD6770My preference is on GTS450 (since I am a CS researcher and using CUDA is a more easier than OpenCL). However I have read performance of GTS450 is quite medicore for FSX (less than 10fps???).I am short on budget so I am limited to above cards or something around those prices.I appreciate your help.