I used to have speaker cables,  untill I found a few meters of F1 PIRELLI electrical cable on the building site I was on.  Man it was hard work getting the banana plugs to fit.  Even through my modest setup, music sounds a bit more airier I suppose,  but in no way was it a chalk and cheese difference.
Here are some vital stat's if anyone wants to know - 
Electrical Resistance in metals: Silver    -    1.59e-8 Ohm-meters
                                          Copper  -    1.673e-8 Ohm-meters
                                          Gold      -    2.35e-8 Ohm-meters
                                          Nickel    -    6.84e-8 Ohm-meters
                                          Titanium -   42.0e-8 Ohm-meters
                                          Aluminum -   2.65e-8 Ohm-meters
So you can see pure copper, like you get in electrical cables but not speaker cables (I've been told there is a reasonable Tin content in speaker cables - must find out more)  is right up there with pure silver, but at a fraction of the cost. (Building site, remember?)