After recently beginning to add the wonderful ORBX scenery add-ons to my system, I'm growing frustrated with my framerates dropping into the teens while flying low and slow over even some of the not particularly urban or dense scenery areas. 

I'm far too spoiled by ORBX to ever think of returning to stock MSFSX scenery -- so I need to consider my options for milking out a few more FPS while not completely reinventing my machine....

With my large viewing area (I have three 22" monitors running vertically, effectively becoming a 42" monitor), I was experiencing reliable framerates of 30+ in typical flying, with reductions into the 20s in dense areas.  I was pretty happy with that.  Now with ORBX added to the mix, I'm finding my framerates are hovering in the mid-to-upper-20s in low flying over rural terrain, with occasional dips into the teens -- and down to LOW teens in urban or scenery-rich areas.  That's getting frustrating.

I'd built my system with the idea that I could add a second graphics card and "Crossfire" the two, at a later time...  But I'm wondering if anyone else here has experience with doing that with FSX, and if the results are worth the bucks.  I'm also finding that the card I have is apparently already out of production, and need to learn if it's possible to Crossfire two similar, but not identical cards... 

Thanks in advance for any feedback!

FSX doesn't use crossfire. No.