It will take a 200mm fan at the top, so space is not a problem, but mounting holes may be an issue.
I really want to install a 140mm WC like the Kraken X40 or the nepton 140XL; this last one can be fitted to a 120mm so it woud fit in the roof ( 1X 200mm or 2X 120 is possible like you said) ,my fear is if the second fan (which again can be 120 or 140mm) will hit something on the motherboard
I could just buy a H80i...but I heard some bad thing about the H80i and H100i....
I'm not too fond of Corsair Water coolers and I too have read about a few people struggling with them.
I do like my Kraken X40.
I don't think the 2nd fan will add that much, but if you *must* have a push/pull configuration, you should measure the clearances. I think most top coolers are not configured in push/pull. One fan should be sufficient.