Yes, power consumption is a consideration for many. You might straightout figure a double in power consumption using a 1+1=2 calculation, but let's just clip on the Clamp Amp Meter to take a look.

Results seen above. During more normal operations, the QX6700 should be consuming about 4% more power in a typical setup, while under intense multi-threading scenario, it can consume up to 15% more power. Do take note that percentages are based over the entire setup's power consumption.