Miui 6.6.16 became very hot even after normal usage.6.6.23 seems to be much better.
You should buy the MI5 ,its SoC is much better and the other specs ,too.Battery life is amazing , mine has about 5-6hr SoT.Overall a great phone.
I used this phone now for good 1,5 day < including 30 min gps.
However i cant confirm that the battery is 3000 mAH.. my battery charger shows about 2200 mAH.. WTF ?
Charging is also Fast ...