I have an alienware 2518hF with 240hz and i have the Problem that in fast motions the screen looks a littlebit blurry and also the edges of the images looks not really clear and if i move it flicks a littlebit. Sorry really hard to explain

Also on white places ingame, it looks blurry when i move it fast.
My settings are:
-dark stabilisation(3, max)
-the contrast on the monitor is set at 30% and Brightness 98% and in the Nvidia control panel i have digital vibrance on 89%
very fast response time(if it goes i wanna stay at very fast because i gives me the best ingame feeling)
-Ingame resolution 1680x1050 streched and quality all low
-240Hz and i have about 300-450 fps ingame (the frame limiter on cs go is really bad and it gives input lag so fps_max 0 is the best)
-I use Display Port cabel under 2m from Lindy Chromo Cabel (or should i use the default HDMI cabel ? )
My Grapics Card is an Asus GTX 980 Strix
Are there any settings for helping me ?
I figured out when i play cs go and i look ingame on the monitor info it says 1980x1080 but the real resolution ingame is 1680x1050 so it uses gpu scaling even if i set display scaling in the nvidia control panel.
To tweak this i can set a custom resolution to my monitor wit CRU of 1680x1050 and 240hz and now ingame the monitor shows the right resolution and also uses display scaling. You can feel it really big differenz that it is much more snappiere and also less input lag.
But the point is that the images are sharper on the display scaling CRU mode but also it feels like it is harder for my eyes to play.