I would buy a second GTX780Ti, too. Beware that you may require a PSU upgrade with it (or you may not, it looks like a sorta borderline judgement call).
I've found NZXT 200mm fans to be very quiet, but haven't tried any other 200mm fans.
If your fans keep blasting at full speed while your temps are low then you might do better with a fan controller.
Another reasonable (bang for the buck) upgrade would be installing a second identical Samsung SSD in striped RAID - whenever you see one on sale.
"All opinions are not equal. Some are a very great deal more robust, sophisticated and well supported in logic and argument than others." - Douglas Adams
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