So as it turns out, I've only got 750 grams of blackberries - probably enough for 2 gallons, just about, based on Daniels. So it seems the majority will, in fact, be raspberry wheat beer after all.
Used Saf-04 to ferment, at 20 degrees C, and it got down from 1.045 to 1.008 in 4.5 days. Must...