Specs similar to Wings of Prey?

[Avimimus]

I'd strongly recommend peripherals (stick and TrackIR), followed by high-speed ram (faster loading times, more aircraft in the air) and CPU - only then will my eyes turn to the video card.

Expect system requirements (in terms of processing) over the first year or two (ie. the next two release will assume 200-300% more power than the minimum requirements - although they will still run without the more power)