sorry, should have been clearer with what i said.
For Siege of Shanghai, compare the DirectX benchmarks at 3840x2160 vs. 1280x720.
FPS at 1280x720 is around 65fps
At the much much higher resolution of 3840x2160, FPS reduced by just 25% to around 48fps.
3840x2160 is 9 times as many pixels as at 1280x720, yet the fps drop is so less.