Best graphics card for flight simulator

What flight sim are you talking about?

For FSX, the graphics part plays a minor role, and the focus is mainly on CPU & Memory speed.

Once the DX10 patch comes out this may change somewhat, but for now the a HD2600 or old GF79xx/X19xx series cards would be fine, heck even the plain GF7600GT and X1650 series would be within the same general performance level.

And I haven't seen an investigation int the workstaion performance, but considering all the compatability issues with the gaming cards, I wouldn't bother with a workstatio card unless you're already using one and just want to try it first if it saves you from buying a new card.