Full blown, a Ryzen 2700x can easily pull over 250w. Add in another 100w+ for the rest of the pc, and 200w+ for a gtx1080 and you are already at 100% psu usage with no headroom for any mistakes. The TXM is an excellent unit, far superior in every way to the 600b, but for an OC 2700x and OC 1080, 650w is a far safer route, even if basic gaming loads only pull 400w. The most energy economical range is @50%-70% load, as is Thermal efficiency, longevity, any leeway for upgrades like more ram or a different drive, stupid little things like additional USB usage for phone chargers (the upto 5A draw for some apple products is still rather large) etc.
2700x and gtx1080 at stock values. OC can easily add another 150w between the cpu and gpu. And Witcher 3 is not especially hard on an 8core/16thread cpu, add streaming into the mix or any other high core use app, and that wattage will definitely jump up.