I definitely over egged these! Some advice online suggested that metering at ISO 3 would produce a good effect. However, after examining the last batch I was fairly sure that ISO 3 would be a stop too far and I was right.
In sunny conditions with a lot of blue sky, I'd suggest f16 at either 1/4 or 1/8 with a R72 filter are probably optimal, but obviously this varies with the situation and development technique. I kept notes on the exposure of every frame, so I'm able to go back and see where I went wrong at least.
The next batch I'm going to expose at ISO 12, with a slightly longer development time because I noticed the normal exposure shot I've been taking at the start of each roll is coming out a little dark on both the rolls of film.