try scan bro, they have top customer service last time i used them for stuff.
http://www.scan.co.uk/
Agreed, but I'm not sure what their service is like outside the UK. Might have export/VAT issues.
Build wise, I have pretty much what you're speccing out. I also made a revised (better) version for a friend.
I agree with what the others have mentioned;
You'll need a decent PSU, around 650W (your system will probably draw sub 500W w/o OC, but it pays to have some headroom and with a decent PSU, you'll probably hit a decent efficiency)
Don't get the WD green HDD (don't get me wrong, it does work, I have one), it's just the cheaper nastier eco version. Red/Black aren't much more expensive, but should pay off in the long run. (Hopefully will last longer :) )
RAM wise, 16gb is quite a lot. I have 8gb and I've never found it to be a bottleneck (I've even run multiple games at once :D). Unless ofcourse you plan to do a lot of rendering or video editing. (Not sure if you've picked a single 16gb stick, 2 x 8 or 4 x 4?)
That SSD sucks, no easy way to say it :p. Samsung is much more reliable (840), EVO being more cost effective and PRO being faster and with a longer lifespan (both have 3 year warranties [Thought it was 7, must have changed]).
Graphics card wise; if you're set on the 780, there are other options. Gigabyte doesn't officially endorse watercooling your card, so if you do that in the future, it may void the warranty. Another option is the EVGA or ASUS who are more lax on it (I think EVGA does endorse it). The EVGA ACX SC would run faster out of the box and is only slightly more, some tests have shown it to run cooler too. Finally the ASUS DCU II, slower out of the box, but with incredible cooling (it's much chunkier and doesn't blow the air out the back, but a good case can handle that) and OCs like a beast (my revised build had this, my friend managed to OC to 1.25GHz and 7GHz effective memory clock).
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/62915-asus-gtx-780-directcu-ii-oc-review-9.html
Wall of text I know :p, one last thing GPU wise; the AMD R9 290(X) with a decent aftermarket cooler are good contenders (though Xfire is still a bit meh). The R9 290 ASUS DCU II and Sapphire TRI X are great (similar temps to the 780 equivalents underload) and tends to OC quite well and it's a bit cheaper than the 780 (should perform almost identically, if not better in some games).
http://www.guru3d.com/articles_pages/asus_radeon_r9_290_directcuii_oc_review,28.html
Same for the R9 290X, except slightly more and even faster. (Sapphire TRI X 290X is about the same price as the ASUS DCU II 780 and will outperform)
http://imgur.com/a/nZUiH
1st is pretty much the revised build I made for a friend (bigger 3TB HDD).
2nd is 290 version
3rd is 290x version
The CPU cooler can be swapped out for a cheaper aircooling one, e.g. http://www.amazon.co.uk/Zalman-CNPS10X-PERFORMA-High-Performance-Cooler/dp/B00350O5DK
(What I use, never had my CPU hit 60C. Then again, I don't OC [yet :twisted:])
Made the lists using Scan (I bought my stuff there (and a past pc too), and my friend did too).