Which size PSU for this system?

[King Mustard]

• Gigabyte Z370XP SLI
• Intel Core i7-8700K (4.9 GHz @ 1.42v)
• 2x 8 GB Corsair Vengeance LPX DDR4-3000
• Zotac GeForce GTX 1080 AMP Extreme (core 1771, boost 1911, memory 2700 MHz)
• 3x drives
  • 2x SATA3 SSD
  • 1x SATA3 7,200 HDD
• 4x fans
  • 1x 200mm
  • 1x 140mm
  • 2x 120mm (on a generic 240mm liquid cooler)
• Asus Xonar DSX

I doubt I'll buy a second GPU in the future.

CoolerMaster PSU Calculator suggests 617 W.
OuterVision PSU Calculator suggests 633 W.