In a comment i wasn’t able to deliver the power consumption for the HP system. However I finally found a Windows license and want to hand in this numbers now: Both systems were configured similary with 4 disks, 4 PCIe-cards, 8 procs at 2.4 GHz and full blown memory (64*8 GB). The Power Calculation tools were configured for for an 100% utilisation. The result: Sun Fire X4640 631 watts idle and 1368 watts at full load. HP DL785G6 needs 1496.23 watts at full load and 794.72 at idle. Update: The numbers for the HP box are for the G6, not for the G5.