Liquid Cooling systems

I am building a box very slowly, but that is because I am getting expensive stuff for it. I have the QX6850 and wanted to know whether it was worth it for me to get a liquid cooling system for it. Does anyone have one? How do you like it? What’s the difference between an internal and external setup? How can I be sure it will work in my case with the QX6850? Any other information that I will find useful?