I'm adding here a couple thing. After the first few full discharge cycles, now it seems like the original 220V USB charger (rated 5V 1500mA) with the USB Sony cable can get the Xperia X battery from 0% to 100% in less than three hours. Using a cheap USB-to-microUSB data cable with the original USB charger, it's way slower (I'd guess Xperia X self-limits to 500mA).