I can only comment based on the assumption that your 100% price spread (£1.5 - £3k) is down to your willingness to pay extra for good customer service, rather than not having firmed up the PC specifications you need.
Good customer service should and does not require you to pay £1.5k extra.
What type of customer support you are after, depends on your knowledge and experience of PCs, including technical competence.
My long retired uncle is still very active and keeping up with all the latest trends, a top silver surfer!!
He owned a series of PCs from large names with good customer service reputations but was still disappointed in various ways; impatience with an inexperienced user, hard to comprehend accents, lack of customer insight and compassion.
He has since been very happy with a local small computer business, from whom he has purchased his last 2 PCs.
As he treats me as his 4th or 5th line support, I've been kept in the loop and he has certainly got good value for his money, considering the very good customer support appropriate for his needs. He has even had free upgraded components just because a motherboard sensor had to be reconnected as well as being mis-set.
But I require a different type of customer support and can save via mail/internet-order, even if it might only amount to a couple of hundred pounds less.
If you could paint a better picture of what type of customer service is important to you, it will help us all to provide better comment.