I strongly suggest you don't watercool and instead buy a new video card, a higher end video card
A very common sense solution from bradhchen. ^^^
The only real functional purpose of liquid cooling is to be able to overclock the gpu and cpu a bit higher.
Comparing the cost of good liquid cooling with the cost of simply buying faster parts might alter your direction.
Also, a 4 way gpu of lower class gpu's will be more prone to microstuttering.
Read this article:http://www.tomshardware.com/reviews/radeon-geforce-stutter-crossfire,2995.html