I have a PC listed in my signature. I bought it only to fly FSX without problems, but it did not solve anything. When I fly the default 737 (everything set to medium with no traffic - air and ground too), I have about 45-60fps, but when I fly the 767, the fps drops down to 8-18fps. I do not fly it, because I can´t. I installed only the flight deck, but it does not help.
FSX is ugly peace of unoptimised software and I cannot understand why it does not work properly on a high-end pc bought five years after the release - it is not normal. I have no problems to set newest games to the highest possible settings and still have 60fps, but FSX - set to lowest settings with no airtraffic and still have problems on the i5+HD5850.
I do not think it is mistake of Captain Sim, but the problem is the software it is made for - FSX.
I really hope the new MS Flight will be greatly optimised and playable without the tweaking circus. I hope MS will do better job with Flight than with FSX. When it will work correctly, I will buy the CS767 for the Flight again, because it is best possible to buy and nothing compares it.
The one thing I can do is to wait for it - or to learn the ATPL in reality...