I haven't touched FSX for quite a while after finishing my race sim rig. I am a huge fan of ORBX & all their FTX regions just amazing quality & the ability to fly VFR if you have local knowledge or good maps. by the way have a look at FTX's newest release,
AU Canberra City Scape. I've been waiting about 3 years for it & it is unbelievable!!!
As for FSX itself there has been some huge improvements over the past 12 months. Now that modern hardware is capable of running FSX at very high settings the shift lately has been to enhance & explore fixes, work-arounds & bugs in the old core MSFS engine it reminds me now of how other sims like GPL & RBR still run today & have a dedicated team of hardcore followers.
For example a new
DX10 fixer product has just been released on the back of the same developer
SteveFSX making many of then freeware on AVSIM.
I haven't tried it yet but apparently it makes for smoother flight at lower FPS & no more OOM's as DX10 can make full use of GFX RAM freeing up system RAM.
Then there is weather, the one getting the most accolades these days is
OpusFSX
Apparently it loads instantaneously, reduced the dreaded cloud pop-up & keeps FPS high even with dense cloud cover.
It also has a live camera so mimics head movement to the environment.
So many FSX users now just use REX for the cloud & environment textures with OpusFSX for the weather injection.
As for tuning FSX checkout
Kosta's Flight Simulation World, he has one of the best
guides to improve FSX performance.