Thanks for the well put together update, always nice when hosts detail what's happened/what they're doing to prevent it.
None of my Manchester servers seemed affected by this - or if they were they managed to keep running through it. Perhaps because they (2 especially) would have been quite quiet then.
In regards to symbiosis, I have upgraded MySQL, just be careful as the latest Debian uses Maria by default, so it will try and replace MySQL with that - I just upgraded to the latest MySQL that was available.
I've not tried upgrading PHP yet as its okay for what mine does, but I can't see it being a problem if it were to be upgraded.