at Overclockers there is also pre oder for 8GB version clocked 1306MHz. So it look like there are 3 versions of that card. 1. 4GB/1306MHz/7000MHz (Nitro+) 2. 8GB/1306MHz/8000MHz (Nitro+) 3. 8GB/1342MHz/8000MHz (Nitro+ OC)

6th August is listed on some stores here but it's not a confirmed date and there's not that many GPU's incoming either it looks like. (Besides for the 4 GB model.)

overclockers.co.uk will probably start sending cards ~5th August. Post from OcUK forum from few days ago. by Gibbo "Right Sapphire have given me some great news this morning, their initial batches that they tested they have agreed to ship exclusively to OcUK in the world. The first batch is a real small number as of course they are not from a full scale production run but a small production batch test run. So OcUK customers will be the first in the world to receive a Nitro+ OC card, the first batch is likely to be around only 30 units and could be with ourselves as early as next Monday!!! Then they shall hopefully ship 1000-2000 units next weekend to ourselves to clear the remaining backorders, 4GB cards should also be in that batch too"

Sapphire RX 480 Nitro + OC 4GB & 8GB Review

The 4GB version is not only equipped with half the amount of GDDR5 memory, but both core and memory speeds are slower too. In the real world, it does feel slower, even at lower resolutions, although by manually overclocking both core and memory, you can get close to reference 8GB performance levels – while saving £50 in the process.

http://www.kitguru.net/components/graphic-cards/zardon/sapphire-rx-480-nitro-oc-4gb-8gb-review/