Different advices

Monitor's settings and configuration

First of all I want to tell about monitor connection - Display-port, DVI (DVI-D), HDMI.
DVI-D (dual link) and Display-port - both are fine and provide less input lag than HDMI, so if now u are using HDMI go for other connection method. HDMI give u more input lag.
BENQ option - INSTANT MODE - always set it ON, because of less input lag.
Many monitors have option called "overdrive", "AMA", usually there are 3-4 presets called as "off", "low", "high" or somth. This option reduce response time, but too high settings may provide "ghosting", u will see black or blue "ghost" behind fast moving objects on screen. Toy with the option a bit to see what looks best.
NEVER use monitor scaling options such as 17", 19", 20" because of huge input lag.

Console commands:

-high - don't use it, can reduce performance. Especially if u are streaming.
mat_queue_mode - set it on "2" just force "enable multi-core rendering", "-1" is auto, so u can change it in "video settings" inside cs.

Eyes Can Only See at 30 fps etc. Same with monitor frequency :D

First off, this is NOT my original work. U can read about it here:

OBS settings:

OBS settings:
OBS settings: