I think water cooling might be overkill, and you can easily achieve cool temps without it, as long as you arent doing crazy overclocking.. or do you just want to give it a shot because you have never done it?
You can also buy aftermarket heatsinks/fans for your graphics cards, so you don't need to replace the entire card if the fan fails.
As far as graphics cards go, the HD4850 and 4870s are a great price/performance option.
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