Spotted by Hardwareluxx.de site, which obviously managed to get some alone time with AMD's Doom demo system based on Ryzen CPU and Vega GPU, the CPU was marked as 1D3601A2M88F3_39/36_N, which suggest that this an F3 stepping with 3.9GHz base and 3.9GHz Turbo clocks.

Bear in mind that this should be the same 8-core/16-thread chip that was seen back at AMD's New Horizon event, but it is a different stepping with 200MHz higher base clock.

The same source also suggesting that the next stepping could bring even higher 4.0GHz Turbo clock, which is definitely in line with what AMD's CEO Dr. Lisa Su said back at the presentation.