Starting with iOS 11.2, the iPhone 8, iPhone 8 Plus, and iPhone X are able to charge at 7.5 watts using compatible Qi-based wireless charging accessories.
Currently, on iOS 11.1.1, the three devices charge at 5 watts using Qi wireless chargers, but Apple promised that faster speeds would become available in a future update. It appears that update is iOS 11.2.
Using the Belkin charger that Apple sells, which does support 7.5W charging speeds, the iPhone X was charged from 46 to 66 percent over the course of thirty minutes.
The same iPhone charged from 46 percent to 60 percent over 30 minutes when using a wireless charging accessory that does not offer 7.5W charging speeds.