Unfortunately I'm very busy with work, but I wanted to take the test with the "/sim/rendering/draw-mask" This is a preliminary test:
PC with GTX 870 graphics card with 6 GB VRAM, 32 GB RAM, quad-processor I7-4700MQ 2.4 GHz
Display: 1920-1050
Airplane: Vitos Su15 last version
Airport: San Francisco Intern. runway 01L
Meteo: Hight Pressure Region
ALS with all max effect
Pilot view
Random vegetation 0.0
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 1" fps 46-49
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 1" fps 52-54
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 1" fps 56-58
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 1" fps 55-57
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 0" fps 57-60
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 0" fps 57-58
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 0" fps 59
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 0" fps 59
Random vegetation 5.0
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 1" fps 39-41
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 1" fps 45-47
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 1" fps 48-55
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 1" fps 54-55
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 0" fps 56-58
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 0" fps 57-59
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 0" fps 59
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 0" fps 59
Random vegetation 10.0
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 1" fps 31-32
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 1" fps 39-40
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 1" fps 36-40
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 1" fps 47-49
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 0" fps 56-58
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 1" & "/sim/rendering/draw-mask/terrain = 0" fps 57-58
"/sim/rendering/draw-mask/aircraft = 1" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 0" fps 59
"/sim/rendering/draw-mask/aircraft = 0" & "/sim/rendering/draw-mask/clouds = 0" & "/sim/rendering/draw-mask/terrain = 0" fps 59
As you can see the aircraft affects for 15-18%. Note that even the trees affect much on performance, especially from the value of 4 and up. If I start from the airport of LOWI, the incidence of trees is much higher, the frame rate decreases to around 20-25 fps with random vegetation = 5.0