Impact of FPS on power consumption.

Malabooga

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.