So I was at my parents over the weekend and doing some hdd diagnostics on my dad's pc, but then he reminded me whilst I was there he got sick of the computer been so slow, (he thought internet was to blame).
I observed whilst he e.g. was waiting for ebay and showing me the stuttery scrolling the hdd activity light was going crazy.
So I loaded task manager, cpu pegged at 100%, hdd not at 100% but busy.
Went to the details tab and ordered by cpu usage, at the top busy was microsoft compatibility telemetry service. We watched it and it went on for 20 minutes until I killed it.
I did the usual, set telemetry to basic, and disabled the privacy and background app stuff in the normal settings.
Disabled a few telemtry services on top of this.
Then went into task scheduler and disabled all the telemetry stuff in that.
Obviously I cannot be 100% with win10 they will never be turned back on (might well be with a threshold update), but now after he boots up and goes in his browser he is much happier, its noticably quicker.
Also installed classic shell start menu and he is now super happy. As he is one of the victims who fell to the silent automated update overnight routine.