FSX is great, but is not available for sale any more by Microsoft.
FSX is available on Steam
Microsoft Flight Simulator X: Steam Edition on Steam
FSX cut themselves a bit short by not allowing your GPU to run your graphics the way it is designed, and instead it loads up your CPU.
X Plane is much better for graphics and flight physics as it is not technically a flight sim in the way FSX is, but is actually used for aircraft design. You can build your own aircraft from scratch and then see how it goes.
For IFR practice FSX is probably the better option, the view outside doesn't really matter when you consider what you are using it for.