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Has very little to do with power. A 1200hp car and 450hp car basically generate same heat at idle. Vettes have issues with low speed/idle, not typically moving. The setup and outside conditions determines what you need.
A 1000hp n2o car will probably run perfectly cool on stock setup. A 500hp car with a big intercooler may overheat on anything in 90+ weather. There is no magic number. See if your car overheats, and address it as needed. External EOCs/TOCs are last line after upgraded everything else.