Looks fine.
Does this bundle make it any cheaper? - http://www.overclockers.co.uk/showproduct.php?prodid=BU-022-AS&groupid=701&catid=6&subcat=2858
Slightly worried the case may not have all the room you really want to do a nice clean install of the water cooling gear.
Phanteks Enthoo Pro which is £79.99 without window or £89.99 with window I feel will take much more water cooling parts and allow you to do a cleaner install.
SLi 780Ti's are also needed to get the best out of 4K.
In regards to Vram I own 6GB 780's and have tried 3GB 780Ti's. I have in every situation got higher fps with the 3GB 780Ti's which would lead me to believe that the 6GB 780's are not worth the extra investment that I out-laid which is a shame but at least it helps for others.
It's not just a question of fps. One of the problems that's been pointed out with 3 GB cards is stuttering due to running out of VRAM. This happens less on 4 GB Radeon cards and not at all on the 6 GB cards. But I'll take real-world reports over artificial benchmarks every day.
I haven't heard of KFA2 before - what are they like for drivers\support etc? I picked the Asus as the board was Asus too.
Is the PSU a bit of overkill?