The problem doesn't have anything to do with JFK.
If you hear the "ding" warning from FSUIPC, alerting you are going to exhaust your memory soon, in FSX, you have no choice other than LOWERING YOUR SETTINGS because, as a 32 bit application, it will never, ever, be able to use more than 4GB or RAM, regardless of much memory in total you have.
And you cannot even use the whole 4GB. Under DirectX 9, the more VRAM you card has, the more system RAM is "stolen" from those 4GB so, the real number is more something around 3.2 GB.
You can try all of these:
- Lower your settings, especially the Max Texture Size slider, the Terrain level of detail range and the autogen density.
- Use the Addon Manager setting to disable 4K textures and go down to 2K or even default 1024x1024.
- Use DirectX 10, it will save about 500-600 MB of RAM
But the real solution, would be moving over to P3D4 that, as a 64 bit application, will never cause an OOM.