Vijseema, unless you're pushing your system to the limit very regularly, or have runs over 25 feet or so, there really is no good reason to use anything more expensive than 18 gauge zipcord.
Years ago when I was running a killer sound system with 8 (yes, eight) liquid-cooled Realistic Mach Ones (with 15" woofers and 27 lb magnet structures), I wired those beasts with 14 gauge zipcord because, well, I was 15 years old and pretty certain at the time that I could melt anything lighter than that with Bohemian Rhapsody.
These days I'm down to four Mach Ones (I don't subscribe to the current "smaller is better" school of thought for loudspeakers...there's a reason that there was no such thing as a "subwoofer" 25 years ago - we didn't need them) and they're wired with 18 gauge zipcord.
If it will make you feel better, or if the runs are long, go ahead and pick up some 16 or 14 gauge zipcord (not at Radio Shack). It can't hurt!
If someone else is paying for it, preferably someone you don't like, pick up the original "spoiled brat" audio accessory, "Monster" cables.
YMMV! Carl