I have to gently disagree Baz. When FSX was launched, Moore's Law on computing speeds was assumed and ACES expected we'd be running 7 or 8GHz processors by now, whereas even the maddest overclockers don't quite get to that yet. Multi-core processing has taken over as the development area in CPUs now.
If FSX wasn't meant to do as much as developers have got it to do then I wonder what the pages and pages of the SDK, published close to ten years ago, are documenting. Reams of A4 in my ringbinder list umpteen simulator variables; yet more pages on SimConnect; extraordinary flexibility to code conditions into animation and visibility systems and the scope of C++ coding and other black arts mean developers haven't yet exhausted the potential for development in FSX.
The limits are the...