If you want a quiet system, don't use so many fans. I'm going to suggest a Coffee Lake system here because although it doesn't have HT/SMT, it does still have 6 cores and a fairly signficant increase in single core performance over Ryzen. For editing videos, Adobe programs tend to be the most popular and they are still more focused on better IPC as opposed to more cores, so the i5-8400 should perform pretty close to the R5, potentially even better.

So, here you go;
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CPU: [ Register or Signin to view external links. ] (£181.98 @ Ebuyer)
CPU Cooler: [ Register or Signin to view external links. ] (£47.46 @ Amazon UK)
Motherboard: [ Register or Signin to view external links. ] (£98.85 @ Amazon UK)
Memory: [ Register or Signin to view external links. ] (£121.98 @ Ebuyer)
Storage: [ Register or Signin to view external links. ] (£134.95 @ Aria PC)
Video Card: [ Register or Signin to view external links. ] (£234.00 @ Aria PC)
Case: [ Register or Signin to view external links. ] (£84.37 @ Box Limited)
Power Supply: [ Register or Signin to view external links. ] (£114.95 @ Amazon UK)
Total: £1018.54

A properly silent system until you start putting the GPU under load. You can get the cooler from Scan for a little bit less than Amazon. GTX 1060 to stay around £1000 since the system you were looking at was £1200 with the GTX 1070. The 6GB 1060 is more than adequate if you're runnig 2560x1080 ultrawides, but I'd try aim for a 1070 at least if they're 3440x1440.