rdustman,
I think your confusing the size (and hence conductivity) of the inner core of the wire with the size (thickness) of the insulation which surrounds that core.
In the case of Magnecor wires, the inner core is the same between the 8.5 and 10mm wires and the impedence/conductivity of the wires (for emi suppression) is the same between them.
The difference in thickness of these wires is strictly due to a thicker silicon coating over the core. The thicker insulation has no direct affect on the electrical energy going down the conductor, but it does provide a little more insulation between the conductor and any adjacent conductors or the engine to reduce any chance of arc-over which would really only be a concern if you are running a very high energy ignition system. The thick silicon sleeving also provides a little more protection against header heat as well.
I doubt that anyone driving a Viper truly NEEDs 10mm wires, since I don't think anyone is running a real high energy ignition system, but they do look good!
PS There may be other mfr. who adjust their core construction between 8.5 & 10mm wires, but I am not aware of them. In general though, lower impedence on spark plug wires does not mean lower performance of the engine, only of the radio
--- Ken
