Hello,
I have the same decision to make in the near future. I the moment i would buy the 760GTX overclocked (from ASUS for example the direct CUE):
here my reasons to buy a 760GTX
- as much GHz as you get will help the FSX (in Boost mode 1250Mhz Core Speed)
-FSX profits more from a good CPU (many tests in past are done with one result: you need a very good CPU and a medium GPU and are have a very good chance to get many FPS)
- low energy consumtion
- up to date arcitcture
for me your system should have a 760GTX overclocked and a SSD and you will have a lot of fun!
Thats my opinion.
greeting