Todd - an 18 gauge twin lead mains cable is rated to handle 10 amps at mains voltage
see
http://www.stayonline.com/reference-circuit-ampacity.aspxAnd - that is continuous power - it can handle much higher transient spikes - and music is just a series of transient spikes - not a continuous current draw - e.g. like an electric motor.
I do not believe your amps, driving your speakers would come anywhere near the current limitations of an 18 gauge cable - even when driving them at insanely high volumes.
Granted, transient spikes could reach fairly high peaks in current levels
But the higher quality signal conductor you are using will handle those fast moving transients with ease.
Once the current is "used up" i.e. by moving the drivers in the speakers - the residual current in the neutral is, by comparison, quite small.
So - you might be thinking that the neutral should be of a smaller gauge at this point ?
Wellll - that larger gauge neutral conductor is required to keep the neutral side "of the entire circuit (amp included)" as close to zero volts as possible. So the "thicker pipe" will conduct that residual current away very quickly
If you are still concerned - you could use 16 gauge for the signal.
To answer your question - my amp is 50 watts (but those are NAIM WATTS) and my speakers are 89db - only one db more than your own speakers.
NAIM is a high current design the uses a large toroid transformer. Even at high levels it’s always been cool to the touch. Which may be an indication that the "real time" current drawer is actually quite low.
Hope that helps :-)
And keep us posted as to your progress