I want the image to be stretched, I planned using Independant Resolution later 
I think 800x600 is now the minimum standard, or maybe 1024x768. But what I want for now, is see how fast my engine is in fullscreen: Windowed, an empty window is 350fps, when switching to fullscreen, it drops to 170fpsā¦ as it is rendering from 800x600 (windowed) to 1920x1080(fullscreen)
All the āregularā display modes are in the list of the supporteddisplaymode of my card. When I play Painkiller for example, I can set it fullscreen at 800x600, 1280x720, 1280x600 etc with image stretched without problem. Iām pretty sure it is not a ratio related problem but rather monogame using displaymode somewhere in its internal code instead of the backbuffer params. Does any Monogameās dev have an idea ? 
Another strange thing, when i set PreferMultiSampling to true, nothing is display, screen emptyā¦ Iāll have to dig into MG Sourcecode to see whatās happening: my code is wrong or MGās is wrong.
Iāve just tested my code with MG 3.5.1.1679 (latest stable) and switching to fullscreen is ok, the image is 800x600ā¦
It seems there has been a regression between these versions.
Another point:
MG 3.5.1.1679 (latest stable) -> 600fps (average)
MG 3.6.0.622 (the lastest dev at the time of this post) -> 350fps
for the same code: a clear, and a simple texture drawn to test the speedā¦