If the coolant level was good prior to starting your lap of the ring then could be thermostat, head gasket or radiator blockage.
Usually the head gasket would blow only after excessive temp was reached, however not always.
I am surprised that you did not slow down as the temp started to climb on the gauge until waiting until you roasted it.
I would fill and bleed the coolant system properly as per the Nissan manual and then carry out your informed diagnoses.
If there is no oil in the coolant or any coolant in the oil you may have got lucky, however like TR I suspect that it may be the head gasket.
Alex.