You should do both.

Speed kills.

Just an example of a car pedestrian accident: at 50km/h the pedestrian dies more often than survives.

At 30km/h, only 3% dies.

I know this isn't highway speeds, and the example is for the city, but I remember Volvo explaining it's nearly impossible to die in their cars up to 70km/h (or close, like 68) but over that there is just too much energy at play.

Also how many seconds are you earning when slightly-speeding? Not very much if you don't drive the highway for hours and hours.

Thank you for reading my ramblings.