It's as good as a single 5870 in FSX and significantly faster in everything else.
As I[ch8217]ve seen firsthand with a 4870x2, no a dual GPU card is not [ch8220]just as good[ch8221] for FSX nor is it significantly faster in "everything" else.
And as far as I've seen in
the majority of application benchmarks by every single source that is actually respectable - like ANANDTECH for example, a dual GPU card is usually significantly faster than a single card. It doesn't mean they're perfect, they have numerous flaws, but they are usually significantly faster.
You have quiet an awesome rig by the way.