The basic choice is:-
1. DIY Build £2,065 ( never built one before :-/
pretty worried about it, but the price includes Scansure Insurance incase I damage anything. )
Skylake i7 6700K, 4 Cores 8 threads, 4Ghz Turbo 4.2GHz, [Passmark Benchmark 11, 000 @ 4GHz - probably not with this fast ram.] 32MB 3,200 mhz Ram, Nvidia GTX 980 II 4GB, Noctua NH D-15 cooler, Intel 750 PCIe SSD 400 GB, Samsung 850 Evo 500GB SSD. Asus Z170 Deluxe MB. In a Corsair Obsidian 750D and swapped out Noctua 140 mm fans to get PWM. Blu ray RW.and Wifi n and a/c , Usb 3.0 Card reader. Be Quiet 1200 watt powersupply single or multi rail options
Windows 10 Home
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Saves £520 


I picked IMO overkill high quality/reliability components, many have 5 and 6 years warranty
Really managed to choose exactly what components I wanted.
Latest technology, say potential to swap out processor in 2 years time for a real boost.
Potentially more powerful graphics card?
Cheaper to upgrade - easier access to info to be able to do it .
Apparently I can overclock it?? Good cooler? Good MB? Good PSU? Formthis.
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I wont enjoy this! Risky using IMO very expensive parts on my first pc build.
Might end up with non-working PC 
Did I select bits that actually will work together
Did I even buy good stuff ( er before my recent research I had never heard of Corsair, Asus, Noctua, Be Quiet etc! )
Or buy a
2. Custom Build by HP - HP Z640 £2,585 .
Xeon E5 1650 Ver3. 6 cores 12 threads, 3.5Ghz Turbo 3.8 gHz , 32GB ECC 2133 Mhz Ram. [Passmark Benchmark 13,498] Nvidia Quaddro K2200 4GB, Intel 750 PCIe SSD 400 GB, Samsung 850 Evo 500GB SSD.
Windows 7 Pro !! Still ( apparently will move to 10!)
Blu ray RW, Wifi only n, I have a/c at home. Usb 3.0 Card reader . 925 watt HP powersupply.
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Much, much, Less risk, except I will install the Intel 750 ...NVME Uefi bios, worries etc.
Higher benchmark, except some say the higher clock of the Skylake is better for Photoshop?
More stable processor. And GPU.
ECC Ram
6 Cores
Proven and tested
4 years on site HP support and maintenance
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£520 more!! A very big premium
Not Windows 10! - will they ever do this? Sony walked away from this on my laptop!
Maybe HP will replace this Xeon range soon with a Skylake ( different socket?? ) Xeon range?
More difficult and expensive to upgrade, getting tech help and expensive bits -
Getting help with say the Intel 750 , will be nasty as HP seem awful. More geared to a business customer.
Wasted £105 on a stupid HP 128GB SSD, no choice.
Expensive adapter plates to convert HD bays, no one at HP even seems to know which ones!
Potentially slower at editing images, ref lower clock speeds ??
Much slower wi-fi - no one at HP seems to know what wifi is available. I guess most servers are locked down on a network eh?
Main applications:- Photo editing, Photoshop, Canon DPP , Portraiture. Note 5DS R raws are 80MB, in Photoshop they hit 160 MB, A bit of 1080p video editing ( Canon / 5DS R amazingly still in the dark ages no 4K 

:
Run Office mainly email using Outlook, bit of web access/research .. Google etc.
Using one 4K monitor @ 3860 x 2160 60 Hz.
I Would love some advice or your thoughts. Yes I could afford the £520 for the HP, but I really would not like to spend it!
Just as importantly, I am not sure its actually a better option.
My main concerns are, I Will screw up the self buid? Especially mounting the air cooler and that thermal compound. 

Balanced by the concern of buying into dying technology on the HP side, with this older generation of Xeon.

