X-plane takes quite a bit of tweaking, my only complaint is that the prop disk drag on reducing power is not well simulated. For IFR procedures training it is very satisfactory. I recently added a Yoke and rudder pedals by Saitek. Compared to a real aircraft they have a large 'dead spot' right in the middle of the range where you mostly fly after trimming out.
The biggest difference in frame rates and quality was when I added a NVIDIA GTX 650 Ti card for about 100GBP. Very much improved responsiveness too.