I just upgraded from a GTX 580 to the GTX 980, gains in FSX, P3d as well as x-plane 10. My old card is a lot older than yours but I have a similar setup. I7 4790k at 4.7 12GB of 2133 RAM. Getting between 40-60 with Orbx Northern California Gold, REX texture direct flying with both the PMDG and the new airbus a318/319.
The increase in x-plane was amazing, went from 32 FPS with most settings in the middle range to 35 FPS with all options maxed out, also using the HD textures v2. I don't really play many other games but I install crysis 3 as a benchmark, and as you said, max everything you're getting crazy framerates. Overall I'd say it was worth the price.