A new review for the Sapphire Nitro+ RX 480, both 4GB and 8GB models.https://www.computerbase.de/2016-07/sapphire-radeon-rx-480-nitro-oc-test/
It's in german so here's a TL;DR by me:
The 8gB is faster by 5-10% by default but loses the edge when both are overclocked (unless a game can utilize more vRAM[Black Ops III saw a 40% fps boost with 8gB vRAM, 77 vs 109 fps]).
The 4gB also overclocks much better than the 8GB card(and they even out in performance when both manually OC'd).
The cooling solution is good but not excellent. The card runs fairly hot(77°C average under load) with noise levels reaching 44dBA which, subjectively, isn't loud but nothing for the enthusiasts quiet pc. According to the reviewer the generated noise has a fairly low frequency which isn't as unpleasant as the higher pitched noise the reference model generates.
You can increase the Temp Target for a noticeably quieter operation. This applies to both cards.
Both cards have 0 fan mode.
Both cards outperform the MSI GeForce GTX 1060 Gaming when overclocked(1060 stock). An imperceptible but measurable improvement.
My personal opinion: the 4gB is the best value card so far. If you want 8gB I'd go for the Strix as it seems to sell for a round the same price but performs much cooler and quieter under load. There is no 4gB Strix.