It depends on a lot more than that, GPM of the pump, CFM of the fans, and really does not go by heat rather the Watts that generate the heat. Then you get into different thickness and fin design, even the reservoir size can have a effect. With liquid your balancing the system you GPU can run a lot hotter than your CPU if your doing a complete loop so your cooling needs to be adequate to keep the CPU temps in range.
Here is a good site for that.
http://www.techspot.com/community/topics/the-watercooling-guide-from-a-to-z.180876/
I would go at least 120mm over what is recommended.