As far as idle goes (the exact amounts also depend on which card you have, custom cards tend to use more than reference cards):
With 60 Hz monitor both AMD and NVidia cards use roughly same power With 144 Hz monitor NVidia cards use almost twice the power over 60Hz monitor, and AMD cards a bit more than 60Hz With 2 60Hz monitors AMD cards use almost double the power, and NVidia cards use a bit more than single 60 Hz monitor With 3 60 Hz monitors NVidia cards use a bit more than AMD cards.
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With 60 Hz monitor both AMD and NVidia cards use roughly same power
With 144 Hz monitor NVidia cards use almost twice the power over 60Hz monitor, and AMD cards a bit more than 60Hz
With 2 60Hz monitors AMD cards use almost double the power, and NVidia cards use a bit more than single 60 Hz monitor
With 3 60 Hz monitors NVidia cards use a bit more than AMD cards.