I recommend going with a better case for improved airflow and if the PC's main purpose will be video editing then Intel is sadly behind AMD and you will be much better off with going with a AMD based CPU.
You might also consider a 64 GB RAM kit which you might need to install yourself since I...
These are the specs I came up with - it will leave you with about 500£ for GPU which hopefully you can stretch to 600£ & get a RTX 2080 Super.
Case
CORSAIR CRYSTAL SERIES 280X RGB GAMING CASE
Processor (CPU)
AMD Ryzen 9 3950X 16 Core CPU (3.5GHz-4.7GHz/73MB CACHE/AM4)
The Outer Worlds -AND-...
Id recommend getting a GPU somewhere else like Amazon, a bit cheaper & better quality companies , such as Asus or Gigabyte.
Stick with onboard audio for the things you have mentioned.
If you would like a suggested specification provide me with a budget and I'll see what I can do.
Do you require...
My bad. I have misread this as a Desktop PC.
Depends really what software you are using to stress test. Prime95 tends to do that to CPU's.
I would still get in touch with PCS & see what they say.
In my eyes the difference between the cores is very worrying.
There is a few possiblities what could be wrong.
The most likely one is the paste not being applied sufficiently and/or heatskin causing this as it moved during transport.
Deffinetly shouldn't be seeing those temps on a non overclocked CPU.
Are you aware what cooler you are running?
Monitor this closely for next few days.
If it is the same core as mentioned above, re-apply the paste.
Or send it back if you don't feel comfortable doing that yourself.
More case fans don't make a difference nearly. Maybe 1/2'C TOPS.
There was a LinusTechTips Video which basically confirmed that.
That spec looks like an absolut overkill if its for gaming :|