Nope...
I found out that I hadn't masked a reflective surface, so it extends way into the distance under water. It really helps with lighting the water, so I'll leave it, but it does cause about 3 more raytrace calculations than normal, with an underwater reflection of the sun that has to be scattered by waves.
I guess it'll be done in a week, but perhaps less, as it's now rendering the final two render buckets with water or reflections in them, and one bucket will finish tonight.