Windows 10, beta (closed) drivers. Probably it throttles, add "-tt 50" option to "config.txt".
UPDATE: my bad, I really see 310H/s in Windows 7 + public drivers. So it is either drivers, or Windows version, I will check it right now.
UPDATE2: it is drivers. If I use public drivers, I can get only 310-320H/s. For beta drivers, I get 440-450H/s. AMD should release new version of drivers asap, current public drivers are bad.
Thanks for the very useful info.
AMD Radeon Vega Frontier Edition (Air)
OS = Windows 7 Professional SP1
Driver = Radeon Vega Frontier Edition 17.6
Average Solutions per Second = 310 (throttles if you let it run for 10+ minutes)
AMD Radeon Vega Frontier Edition(Liquid) / RYZEN 7 1800X or Core i7-7700K
Will try later tonight with Windows 10 Professional or Ubuntu 16.04.3 LTS with beta drivers and report back