I'm wondering (as always) if the fastest conquest route is an Astro beeline. With no circumnavigation, this time galleons double our movement over galleys in addition to saving extra turns by going directly across ocean tiles. Furthermore, we're philosophical, so we can generate the GSes even faster. Of course, the galleons are also much safer against galleys and triremes and carry 50% more units.
I've noticed that by the time we get our first GS, the academy or super spec only saves us about a turn on math. Our capital is not particularly commerce rich. I'm wondering if we even want to use our GSes that way at all. What if instead we grew our empire to 1AD and had Astro at the same time?
I'd be okay with going after Astronomy. If it does look like we can settle Canal Cities, I see nothing wrong with razing many AI Cities except for Canal-based ones and keeping some of those Canal-based ones (and bringing along the odd Settler with our war parties in case the AIs settled 1-square-away from where a Canal would fit).
It certainly would be easier than shuttling troops down an isthmus and then up an isthmus over and over again.
I don't think that we can get Circumnavigation on a map without world-wrap though, right? Still, Galleons with 4 movement points and the use of Canals Cities (plus Forts, as required) could be a quick way to win a map IF the rest of the map looks like our area--if the rest of the map is one big Pangaea and we only have an isthmus just to make a Cultural Victory easier, then things would be different.
It will really help to be able to see if there is an indication of:
a) Whether or not one more "hub" exists... if one more exists, then we can probably safely assume that all of the AIs have hubs
b) Whether or not it looks like there are thin isthmuses to hubs (assuming that there are hubs)... if the isthmuses are thick, then we can't really make effective use out of Canal-Cities, since building multiple Forts takes time and might not fit everywhere if an isthmus is 4-squares-wide
c) Whether or not said potential hubs are connected to the edges of the map, potentially negating the need for Canal Cities if we can sail around them
I think that ONE Work Boat exploring in a randomly-chosen direction will be a good way to check for a), b), and c), without commiting too many resources to early exploration.