1) That is one of the most useless spec sheets I have seen. Their graph shows 63 degree rise at "full load" without even a whisper of what "full load" might be. 1 Watt? 1000Watts?
2) I'm not sure I understand. Are you proposing taking a chunk of copper (I don't think something 10mm thick qualifies as a "sheet") and drilling holes through it and running water through those holes? I think this would be a fairly complex calculation: what is the water temperature? what is the flow rate? What are the dimensions of the holes, their spacing etc.