I'd go by the color of the resin pistils. Jorge Cervantes writes in Mariijuana Outdoors: Guerilla Growing, "Peak harvest is when half of the stalked resin glands are translucent and half-turn amber."
what johnny said was dead on,its hard to tell from your pictures but usually best when the pistils have MOSTLY turned colour...I pluck when they look like they're about %80 turned orange/red/brown