This is what I'd do if i were you.

First, set optimal system settings.

Then type the following console commands.

cg_fov 80
com_maxfps 125
cl_maxpackets 100
snaps 30
r_drawsun 0
r_drawdecals 0
r_lodscalerigid 4

Sorry i cant provide the details of the commands cause i forgot them but check Google.