By now, i'm sure you have seen some of the latest screen shots for Flight Sim 10. If not, take a look at FS Insider. This has brought forth alot of questions in regards to hardware support and what type of shader hardware is required to take advantage of the new visual features. Of course, keep in mind that we are still working on the product and things may change but here is my current point of view.
Architecturally, our rendering architecture was designed to be flexible and take advantage of the current hardware setup. Our main shaders are essentially components (such as lighting, bumpmap,...) which are pieced together and pushed to the hardware. The features used and put together generally depend on the detail settings and the underlying hardware on the machine.
Functionally, 2.0 and 3.0 shaders are mostly the same. One of the main difference being from a performance point of view and also in terms of the maximum number of instructions that a shader may use.
Under most circumstances, our shaders fit well under 2.0 shaders but there are a few cases where we can exceed the maximal number of instructions and turn features off. These cases would benefit from 3.0 shader hardware, but they are rare.
Now, from a performance point of view, 3.0 hardware is generally more performant and will of course yield better graphical performance. But a consideration that is probably more important is that Flight Simulator is a memory hungry application. This is even more true now that we are increasing the texture resolution in the game. Even on a 256MB card, with the settings cranked up, we run out of memory on the video card. No worries, we are smart about it and implement level-of-detail schemes to ensure the optimal use of the video card memory.
In fact, our performance on video cards is generally more bound to bandwidth usage (to transfer textures and geometry) more than shader bound. This means that you may have a better performance benefit in Flight Sim from going to a video card with more video memory rather than a card which can do faster shader operations. This is a consideration to keep in mind if you prefer to texture detail over various visual effects.