I'd take the trade. 60+200 for 250+100 isn't bad, and we find out where the iron is. The hill N of the stone would be a decent city site, at least in terms of food. Lots of sea tiles--good place for Moai? Looks like we're going to get our hammers' worth of exploration out of the frontier warrior--how far does this continent go?
Let's keep an eye on Shaka's settler and galley. I think that in BtS you can't see what's onboard ships. If it looks like he's headed toward our stone island should we close borders to stop (well, delay) him?