Powering 25 x 5 volt 1.5 amp devices
I would personally cluster them into five groups of five Arduinos each, with one power supply (5V 8A) per cluster. If you power them all from a single supply, any time the power draw on several experiences a coincident peak, the power to all of them will drop momentarily and you may see CPU dropouts, even with very large busbars carrying power to the Arduinos. In addition, if you lose a power supply (all the magic smoke drains out), I'd personally rather lose the functionality of five of the Arduinos than all of them, and I'd rather replace a failed 8A power supply than a failed 40A one.