Thanks DaveMcW, what a great idea to move the settler west! I think that a granary in 3350BC and settler in 3150BC is even possible, using only tiles which are fully visible at the start.
klarius, it is tempting to sneak in a "chopsqui" (thanks Horragoth

) before the granary. But I do think the delay is significant - it looks to me like a three turn delay in production of the settler, at 3000BC. Which might be worthwhile.
On the question of whether one Chasqui is as good as two warriors, I feel that the answer is yes for exploration. Two warriors cannot travel twice as far as one warrior. The Chasqui's greater speed should improve the odds of opening more huts. I've tested the Chasqui a bit and found something disappointing - although it can use its second movement point after moving onto a hill or mountain, it does get stuck in forest and jungle. This sure seems like an overpriced UU at 20 shields. And if there's a lot of forest/jungle then sending out warriors could be better.
On the issue of walking a long way for more bonus food: this start is a lot different from COTM02. There we were an agricultural Civ on a barren peninsula without a river. As we explored, each step we took improved our position by enough to at least break even on the time lost taking the step. And getting to a river alone is worth a few turns of walking for an agricultural Civ. Here we're an agricultural Civ with a fairly rich start position and we're already on a river. Unless each step the settler takes can be seen to be an improvement, why risk it?
I plan to start by moving the scout NE and (if nothing startling at that point) N to the hills. If that reveals something nice then I'll probably pause for a long time to compare the potential with DaveMcW's settler W idea. Might go for more food, might stick with the original plan. If the scout doesn't see food from the hills then I'll definitely move the settler west. And unless that reveals something startling my worker will clear the forest. In the next few turns I'll decide on whether to go straight for granary and settler in 3150BC or to do a chopsqui first. If the new tiles revealed to the north and west when settling create more options (even a BG in the town's initial radius might make a difference) then I may change to do a chopsqui, and if the first scout doesn't find a good location for a second town then an additional explorer will be a higher priority. I might even follow the granary or chopsqui by a worker before settler. All depends on what settling and the first bit of exploration reveals.
Research: I plan to research flat out, starting with Alphabet and taking the usual Conquests path to Republic, i.e. Writing, Code Of Laws, Philosophy, and free tech Republic. If the scout gets to pop a hut before my first turn of research I'll block a research path other than Alphabet while popping. I've never popped Alphabet at the start but I remain ever hopeful!
