What I notice is that marginally the clips do work better in all conditions. Mostly not because of the hookup ratio but because when a fish does get hooked the clips always work but sometimes the rubber bands don't break.
On days when a lot of fish are not getting hooked up on the boards, the clips don't hook up any better, they just pop off quicker.
I agree with Skip. Speeding up the boat sometimes helps. It either weeds out those lazy inagressive strikes of just makes the fish bite better for some reason.