I did a fresh install 18 months ago into a new machine Sandy Bridge 2700 K overclocked to 4.4, GTX 580 since upgraded to a 780, with four monitors and Saitek/CH hardware.
I have tweaked FSX using Kosta's guide, installed a ton of addons and have crashed maybe 6 times, in most cases traced back to scenery glitches, for example at Orbx's CZST if I take the first canyon to the northwest I will crash FSX every time. I also ran out of memory once, turned down the autogen and have not had that problem since. Other than that, smooth flying. I avoid freeware scenery, commercial tweakers, shaders (lathough I am flying DX10 using Steve's DX10 scenery fixer) and anything that tinkers with the core of FSX. Maybe just lucky but my experience has been very good. Keeping those ole fingers crossed