What sized case for SLI GTX 780?
My friend is getting SLI 780s, what sized case should he be looking at? Mid tower or full tower?
As previous have said, many cases could support the GTX780, you will just have to look at the specifications, they will often specify the maximal graphics unit length capabilities.
Considering it is a fairly high-power consumtion component, your friend's choice should be one that could support this setup effectively.
A very small case doesn't allow a lot of space, and air-flow capabilities are limited. A midi tower allows for a lot of airflow, and it is big enough to make room for good cable managment. A full tower requires quite a lot of fans to have sufficient airflow, although may be an excellent choice for watercooling equipment.
If temperatures and extreme performance isn't an issue, he should be able to use any size of case he would like. Generally midi tower is a good choice if you don't have any specific needs (e.g. need it to be small or big enough to fit your watercooling system or 3x GTX780 SLI setup).
Anything smaller than midi probably won't fit both of them. For both of them I'd go for a roomy midi tower. I have built SLI setups in both midi and full, and albeit full was significantly easier to work with, the midi is sufficient.
Again, the full towers allow too little airflow, so the temps on the GPUs may suffer. If your friend is going all out, sure, 800D is a good choice, I have it myself... But that's because I have an extreme watercooling setup. If it was for any other reason I would've picked a smaller case with better airflow... and one I could actually carry under my arm
Hope this helps.