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Good Morning to You ALL !
This is our big day
Our most expected day
Android 6 MM has landed on our Xperia Z5
FW is 32.1.A.1.163, so it contains a lot of bugfixes with introduction of MM 6 Android
Right now, is rolling for different models and on different countries so in few hours, or in one or two day, it will be on your phone, unless u're on a branded-operator phone where u should wait more days to come
So, 7th March was right as we expected based on TWITTER INFO by Sony Xperia GB 
More news to come !
Marshmallow is awful. And after being a loyal Sony customer. My Z5 is my last Sony phone.
To be fair, us Sony users are most definately not the only smartphone owners having issues with the update to Marshmallow. Even owners of the latest and greatest Samsung Galaxy S6,7 phones, LG, even Google's own Nexus devices, are reporting multiple problems with their updates, many of them identical to ours, which likely points to problems with Marshmallow itself rather than solely Sony's implementation of it. Also the infinite variations in hardware and software is bound to cause problems that weren't previously obvious. So to those saying "This is my last Sony phone ever", all I can say is best of luck to you, most likely the only way to 100% avoid issues with upgrades might be to get a feature phone instead of a smartphone. 
Personally, I will upgrade at some point, new shiny stuff is fun, but not until I'm confident the benefits outweigh the pitfalls and the device will remain as reliable as mine currently is. After all, most of us have lives that revolve around or even depend on reliable communication. It's encouraging to now hear of some people who have had success with their updates, hopefully they'll keep us posted in the days ahead as they discover more, since, I'm (and I daresay, many others?) interested to see how they go? 
As always it is very hard to determine if there are actual issues with the software or if it's just a very vocal minority with issues down to being special circumstances.
Now hearing that not only Sony phones have issues confirms my approach of being sceptical as long as reports of customers having issues pop up.
I've updated my z5 to 32.1.A.1.185 (what took Sony so long... and still turn out to have bugs that should have been caught) and have been bootlooping after every restart.
A fix is to remove the sd card + sim tray before turning on and reinserting after boot completes. After the sd card is detected and scanned/fixed, the subsequent restart no longer bootloops.
Issue seems to be sd card related. Have yet to try formatting my sd card to see if that stop the bootloop permanently.
I installed PC Companion and update was possible from this program so if you are waiting for the update notification from your provider then maybe this is the way to go.