The results with the Phenom II X4 840 are not directly comparable because for our new test rig we upgraded the power-supply to a more efficient one with 80plus Gold certification, which resulted in 1-2% better results for this CPU.
With a little less VCore on default, it does help the CPU to achieve a better performance per Watt also due to the higher clock. Not all CPUs/chipsets have onboard graphics, so the i5-750 runs with our good old HD 4850.
With four or six cores active Cinebench shows us the efficiency of the whole system. Of course without a graphics-card efficiency is better:
Naturally the more you overclock with voltage increase the worse the efficiency will be.