I have the 800D case too and I am readying my watercooling loop. Here is what I have concluded to after seriously alot of research:
-You can use a reservoir/pump combo such as the XSPC reservior+twin D5-vario pump combo. For the 800D especially it is very convinient, as MT Alex shows in his picture.
-In any case, I would go for 2 pumps for a system that will cool 2 GPUs (and make sure you put the 2nd pump in a critical place in the loop (though using a dual pump +reservoir combo saves u alot of trouble)
- The Koolance 380i CPU block is the best performer by far and XSPC raystorm and EK supermancy are also good in performance and most importantly for me appearance.
-DO NOT, i repeat, DO NOT buy the XSPC Razor VGA waterblock, it is total trash. I am thinking of using EK or Koolance blocks depending on my cpu block choice.
-I am going to buy a Black Ice SR1 360mm radiator and a slim 140mm for the rear.
-I will buy more 120mm fans from corsair (SP120) as they are top performers and i am thinking of using NZXT LX dual bay controller
-Using this controller plus dual bay reservoir is a good investment in terms of space... since I dont use front 5.25 bays anyway.
-You can consider cooling the mobo with a full kit but it is more for the looks rather than performance, since the mobos will do fine with even active cooling.
-Same goes for RAM, though i plan to watercool them for the looks mostly.
-I considered using colored tubing and the simplest/purest possible liquid coolant, but i am not sure on that yet.