I always book the boat first.

The 50-100 days out is pretty much what we've experienced (about 12 data points) but I don't know about spring break. I've given up on the hope of lower fuel prices ever lowering fares. From what I've read excess capacity would be the only reason they'll lower fares. The extra revenue will be used to lower operating expenses which will increase profits. Basically, that means buying more efficient planes.

For last June-July, 6 months out we booked a big cat and were flying kids in from Europe (we were coming from the US) - we wanted everything to go as planned. We waited a little on our airfare, it went up, we chickened out and bought ($976/pp), about 60 days out they dropped to $746. I'd still do it again, the increase in airfare was a drop in the bucket compared to what the big boat cost us.