I don't think people appreciate how smooth 15 fps is in FSX (although I always get more than that) compared to FS9, and how good things look with the sliders far from all the way to the right.  And actually, you can run nearly every slider all the way to the right, see Nick's setup guide.  I use REX with 100% clouds for a skyfull and Traffic X at 50-70%.  You have to use some common sense and make compromises for certain premium products ;-) but it is nowhere nearly as dire as you think. aal is right: the days of "needing" anywhere near 40 fps are long gone with FSX.

Having said that, I'm glad you're happy with your platform and it is indeed a good one for big iron.  Without a CS767 is just became a little less good, though.