motivated by that discussion, I took the direct comparison yesterday night;
I took the MAAM Avenger from Wr Neustadt to Vienna Intl, using FS9, Austria Pro Scenery, Austrian Airports, UT Europe and GE, approaching from the South and taking the direct approach to RWY 34;
the result looks stunning on my PC;
the same route, taken in FSX using the Acceleration Mustang produced an enjoyable flight, but the scenery does not look anywhere near the above mentioned combination, even when using Austria Professional X and UT Europe;
afterwards, flying short hops with Tongass Fjords, the situation changed vastly with FS9 looking nice, but FSX blowing that experience out of the water any time;
it really depends on where you want to fly mainly it seems therefor;
for Austria, my initial statement still holds true, but for areas where there are dedicated FSX sceneries available, given your way better PC specs, the situation might really look much different

as soon as I have FRAPS up and running again, I might post some pictures to show the differences;