I don't agree with kelthic. I would put it as an intake. Yes it will warm your case a little bit, but the HAF X is very airy.
Also, placing it as intake will create a positive pressure in your case, which is a good thing : it means less dust in your case.
I have a HAF X and I used to have a negative pressure inside my case, which was always very dusty. Then I changed my fan setup to have a positive pressure and since then I have almost no dust in my case.
I don't see how neg/pos pressure affects dust - air still comes in the case (maybe less with neg pressure) - filters will help with dust. To get max efficiency out of your H80 - should be an intake. If you want to keep the case temp down (gpu cooling), exhaust may still work for you if the cpu temps are ok. I had my cooler as intake and changed it when I added another gpu.
I don't see how neg/pos pressure affects dust - air still comes in the case - filters will help with dust.
You should read this article on Tom's Hardware. It explains very well the pros and cons of negative vs positive air pressure.
Normally, I'd recommend having a negative air pressure for a case, but the HAF series from Cooler Master have lots of holes in them, so air can get in from almost everywhere. With a negative pressure in the case, air from the outside will be sucked in from those holes.
However, if you have a positive air pressure, it will be repelled. So if less air comes in, there will be less dust. As for temps, I've seen no discernible difference between positive and negative air pressure.
EDIT : also, since you have an H80, which is a radiator, the internal temperature of your case is of no import if you put it as an intake, since it will take its air from outside the case.
It will take cool air from outside and the heated air goes in the case. \
Edit:I think that article over simplifies neg/pos pressure. If you have 2 fans at 60 m3/hr and one exhaust at 120m3/hr in an air tight case - that 120 fan will actually be pushing much more air than rated. The total amount of unfiltered air flow will determine how much dust there is.
It will take cool air from outside and the heated air goes in the case.
Which will be almost immediately sucked up by the 2 giant 200mm top fans placed as exhaust. So it's not really a problem.
However, if you didn't have those 2 big fans, then it might have affected the internal temperature of your case and thus caused a small increase in GPU temp.