The way I've heard it, as a very imprecise rule of thumb, increasing clock speed scales power consumption quadratically, while adding CPUs increases power consumption linearly. So, very roughly speaking, one 1.6 GHz CPU uses twice as much power as two 800 MHz CPUs.
The equation for CMOS switching power (as opposed to leakage power) is
capacitance * voltage^2 * frequency
but the voltage limits the clock frequency. The exact scaling of maximum clock frequency with voltage depends on the circuit and the process, but from taking a glance at the voltage tables it looks like the main cores in current Snapdragons are generally running in the 0.8-1.2v range across their entire frequency range.
Most of the power differences between cores these days isn't in terms of clock speeds but in terms of extra structures that cause more instruction to be executed each cycle. The rule of thumb involving voltage/speed scaling is that your power use is indeed the square of your performance more or less when you're in a reasonable region. However, a relatively simple in-order core like an ARM A7 might also only take 1/4 the energy to execute a given instruction of a complex out-or-order core like an ARM A15 even when both are clocked at 1 GHz on the same process.
