I'll admit I stumbled onto this by accident after connecting my 780GTX, via HDMI cable, to a Sony XBR43X800D 4K model. I now launch FSX at 1920X1080X32 and then switch after startup to 3840X2160X32. While I don't fixate on my FPS values, this combo has given me the smoothest scenes without tearing or other artifacts. I left the Sony set at 1920X1080 (the recommended setting). This smoothness and high FPS is achieved with all Orbx Vector options checked, Orbx Global, etc. - I run AS16 and pretty heavy load of installed scenery. I am also running DX10 fixer and NI with this setup. AA is set in the sim.

 

I haven't had the time yet to dig into the nuances of 4K displays, but is there a layman's explanation for why this combo works out well?

Nice monitor I have one - luv it

I now realize what my stumble was...I upgraded Nvidia drivers, but forgot to reapply my FSX 10 settings in Nvidia Inspector. However, I find that I can maintain high FPS and sharpness without NI if I select 3840X2160X32 within FSX (after the free flight setup loads), leave my 4K tv set to 1920X1080 (default).

 

So while there is the slightest of shimmering, I have sharp edges on the aircraft models and a very responsive sim.  Not sure at this point if there is any need for NI with my setup (also running DX10 mode with Steve's fixer, 780 GTX card, 4790K CPU.) Just an idea to try if you are fooling around with a new 4K monitor or tv.