A 480mm would keep them ice cold, but a 360 would do just fine, and I personally own a HAF X for my main rig right now and they are very very spacious inside. I think I have seen some people put 480s in the top, but I'm not sure. I have a H100 (240mm rad) and it fits with room to spare. A 360 would fit up top just fine, might require a little modding. As for the 800D, I have never personally built in one, but I have a buddy that has one, and it too is a massive case, I'm pretty sure that you would not have a problem mounting a 360 in either, as for mounting outside, you can always get a rad bracket off of FrozenCPU that would attach it to a 120mm fan slot. Hope this helps!