TweakTown has put forth an article wherein they claim to have received info from industry insiders regarding the upcoming Vega 56's performance.
Remember that Vega 56 is the slightly cut-down version of the flagship Vega 64, counting with 56 next-generation compute units (NGCUs) instead of Vega 64's, well, 64. This means that while the Vega 64 has the full complement of 4,096 Stream processors, 256 TMUs, 64 ROPs, and a 2048-bit wide 8 GB HBM2 memory pool offering 484 GB/s of bandwidth, Vega 56 makes do with 3,548 Stream processors,192 TMUs, 64 ROPs, the same 8 GB of HBM2 memory and a slightly lower memory bandwidth at 410 GB/s.
The Vega 56 has been announced to retail for about $399, or $499 with one of AMD's new (famous or infamous, depends on your mileage)
Radeon Packs. The RX Vega 56 card was running on a system configured with an Intel Core i7-7700K @ 4.2GHz, 16 GB of DDR4-3000 MHz RAM, and Windows 10 at 2560 x 1440 resolution.