I'm mostly playing for (quick, below T160) science victory and, regardless of difficulty levels, I now believe that it is essential to either start with a scout or builder/settler combo as it provides the best return.
For far too long, I've been stuck with slinger/slinger opening, especially on deity, without realising the benefits of an early game scout: namely:
* on some maps, having a scout is the only way to hit a eureka for Political Philosophy (how many turns of culture does that save?)
* in most games, the scout will hit at least one goody hut boost (or a builder) that will save you turns of research/science/production
* I can't remember when was the last game I played that the scout did not steal at least one settler, and in most games two or more (I do try to make use of aggressive scouting and wandering into enemy territory) - which is a huge benefit early game.
Additionally, unless there is imminent threat, having an early settler before starting the slinger rush is a must - putting your second city up before T20 is just a huge edge, and will extremely speed up your expansion (through giving back at least 2 extra settlers) once you slot in colonisation.