Ok I'm on the edge on my technical knowledge here but my understanding of orthopanchromatic is that it's less sensitive to red like the Efke 25 & 50 films. I've not heard of anyone having problems changing those out of direct sunlight but might be wrong.

Using a film through a range of speeds I don't think will be a problem as I've been rating HP5+ from 200 to 1600 without any problems.

As mentioned earlier I think we will have to wait and test a couple of rolls to see how it works and if it comes up to scratch as an alternative.