I use one screw per Fastrack section. What with the known issues of electrical continuity I don't want that track moving at all. I have learned to be very cautious and to draw screws down until the track is juuuuust snug on the decking, most especially if a screw is applied to a track switch (which happens only when adjacent track sections don't have screw holes).
At the switching-speed trains mostly move on the PER noise just isn't an issue. I enjoy listening to the wheel-clicks on the rail joints and with locomotive sound on at low volume everything sounds good to my ear.