Thanks for the reply David.
The product is a publication that is available as an E-Product that can be downloaded but also as a standard physical hard copy that requires delivery. This is why I thought the option categories were a good fit as we would create a product in the store with a price of say $45 and attach option categories for both formats - hard copy and soft copy, both with an additional price of $0 and add a delivery option for the hard copy. The soft copy option would represent an E-Product and the hard copy option would represent a standard product.
That does seem to work in practice but it just feels like that is not how option categories were intended to be used and if we go down that route I don't want to cause more pain in the future as we get more familiar with the E-Commerce application.
We did look at variants but delivery is defined on the product and not the variant so the downloadable product would get a delivery charge, although I guess that could be customised.