I went with Crucial 8GB sticks, the 16GB sets are out of stock until the 21st according to web chat yesterday.
I had following reply from Cruical support regarding pricing of pairs and individual modules:
Individual modules and kits are classed as parts in their own right and are priced accordingly. Generally the kit part will be priced similarly to the price of the individual parts that make up the kits. For example, 1 module £10.99, kit of 2 modules £21.99. However there are times when the difference is slightly more.
The reason we offer kits is that these are guaranteed to be a matching pair from the same batch, this helps for running memory in dual channel systems. If you buy individual modules they might not be from the same batch.
Also under the warranty the full kit is covered, so if one module was to develop a fault we will exchange the full kit for another matching pair. If the modules are bought individually we would replace the faulty module.