I'm happy to report that battery life on WIUI 3.6.14 is pretty amazing. It's been almost two full days and I still have about 40% battery left (am using extended 3120 mAh battery) so with my current use, I should be able to go over 3 days with no problems. Albeit the use has been relatively light (only a bit over 2 hours on screen time), but I've still been making phone calls, texts, checking notifications, taking pictures as usual, with a bit of gaming, viewing YouTube videos, and streaming some online radio via 3g. Wifi is on all the time and I have my phone on Normal Mode with about 80% brightness. I'm also running Greenify in conjunction with Tasker so my phone is in Deep Sleep almost 90% of the time.
The only minor issues I'm having is that some apps aren't working properly, like SwipePad and Stick-It Player, but I can live without those. Another couple of tiny issues I noticed; sometimes Twitter will be stuck refreshing and the trending section in the YouTube app doesn't refresh itself, but again, it doesn't bother me, I just thought I'd mention it. All my important apps are working.
Eventually I will see how much on screen time I can get with this. On 3.2.22, I was averaging 5 to 6 hours a day and could stretch it up to 12 hours on Power Saving Mode with a dimmer screen and I would only need to charge once daily.