Steve, as we've pointed out(along with others)on numerous previous occasions, that sort of advice in the manuals about a lower impedance switch or menu setting may be fine for keeping the UL happy by possibly limiting overheating, but it's terrible advice from the standpoint of maximum performance and should be disregarded. All it does is to reduce the maximum voltage that the power supply section of the receiver can output, and following Ohm's Law again, when the voltage is limited so is the current(I=E/R)and the resulting maximum power output capability(P=IxE). Tests such as those by S&V indicate that typically the output is roughly cut in half.
Also, in considering how much current a speaker uses at a given sound level, speaker sensitivity has to be taken into account, and a speaker such as the M80 with slightly above average sensitivity can actually require the same or even less current for a given sound level than an 8 ohm speaker of less sensitivity. For example, if the M80 required 50 watts for a brief peak, the current required would be (square root)50/4=3.53 amperes; for the same brief peak a speaker of 3dB less sensitivity requiring twice the power(e.g., the M3)at 8 ohms would similarly require (square root)100/8=3.53 amperes.
