Fire GL cards are aimed at professionals working mostly with OpenGL graphics. Computer games, like RealFlight, use a different API, DirectX, which has somewhat different requirements to video card hardware (i.e., the fastest OpenGL card may be not the best card for DirectX).

The choice of video card, besides obvious monetary considerations, is also a "religious" matter. Some people swear by ATI Radeon cards, while some other buy only nVidia GeForce cards. I've tried both and, while both deliver good performance, nVidia drivers seem more stable and troublefree.

To find the best price on PC hardware, you should read other forums, like Anandtech Hot Deals or FatWallet Hot Deals:
http://forums.anandtech.com/categories.cfm?catid=40
http://www.fatwallet.com/forums/categories.cfm?catid=18

Good luck,
Boris