Someone with access to an RX Vega sample tested Firestrike on it, The listing does not tell us which RX Vega is this and in what mode. GPU is clocked at 1630MHz and memory at 945MHz same as Frontier Edition. But it has 8GB of Vram.
There are total 3 tests, performance either on-par or below that of the GeForce GTX 1080, but comfortably above the GTX 1070. Tested on Core i7-5960X.
Take it with grain of salt, RX VEGA is launching on 10th of July at Siggarph. There are no custom cards at launch. The scores are 4 or 5% better than Frontier Edition in 3D Mark Firestrike performance test as we seen before. Optimized drivers and tweaking can take this Vega between GTX 1080 and GTX 1080ti.