Big thanks for help, seems like closing or minimizing fullscreen program
doesn't freeze screen anymore (it was biggest issue for me).

I've added 2 files to xorg.conf.d:
20-radeon.conf (this one solved the freezing issue):
Section "Device"
   Identifier "Radeon"
   Driver "radeon"
   Option "SwapBufferWait" "0"
   Option "DRI3" "3"
EndSection

and 20-intel.conf decided to stick with intel driver:
Section "Device"
    Identifier "Intel Graphics"
    Driver "intel"
    Option "DRI" "3"
EndSection

Actually I can't tell if intel is using DRI3, the output from xorg logs is the
same. I will also try modesetting driver to see if it does anything.