I run both FSX and FSX-SE on Windows 10 with reasonable results.
I did move to an SSD for the main disk holding both the OS and FSX / FSX-SE. I put most add on scenery on an additional HDD.
I run with a lot of AI (most major commercial airlines, GA aircraft and a selection of the MAIW military AI) and 3rd party add-ons (most ORBX products and freeware associated with them plus freeware Norway and South Africa)
Framerates are locked at 30 and usually are around there (down to 12 - 15 in busy areas like southern California and southern England) but the game is usually smooth enough.
Just to give a level set I have been timing load times ever since I re-installed on the SSD
Clean install of FSX + Acceleration - 34 seconds
Clean install of FSX-SE -40 s.
FSX-SE after installation of FTX Global, Vector, OpenLC, FreeMesh, civilian and military AI - 4.36 min booting default Cessna to Schiphol.
FSX after installation of all FTX Regions, several FTX payware airports, civilian and military AI - 5.46 min booting default Cessan to Compton Abbas
I have found the biggest issues with regards to stability are
1) AI - if there are missing aircraft in flight plans, missing textures etc this causes the system to spend time searching and trying to render no existent things. the best tool for fixing these issues is ACA-2013
http://aifs2.pvdveen.net/?p=233 It runs thru your FSX install and identifies all the issues.
2) Overlapping Airports. Sometimes I get conflicts between different 3rd party scenery packages and have multiple packages trying to render the same airport. The best way I found to resolve these is to back out packages until the system becomes stable again and then troubleshoot.
No idea if this will help Cees.
Thanks
Gavin
PS my system is an old I5 Gigabyte system (mildly overclocked to 3.2 GHz) with 12 GB RAM, GTX970 GPU, 500 GB SSD & 500 GB HDD. So not exactly a screamer but not bad.