Zar, It all depends on the gauge and length of the wire. Short wires on heavy gauge is best. The longer the wire the heavier gauge you have to use. If you already have short runs of 8 gauge wire or larger adding more will not be a benefit and may even hurt as you will be increasing parallel resistance (google it for an explanation.) IMHO Kimber Cable makes the best speaker wire. Their construction is brilliant because it keeps both parallel resistance and induction to a minimum and you can choose your series resistance by gauge. You can also buy it in rolls. Just a warning to those considering this, it is a PITA to terminate. It is not hard and it is worth it but plan on breaking a few finger nails.
