03-24-15: SoixA technical correction to Soix's otherwise excellent post: Doubling the cable will double the capacitance, everything else being equal. That is true for both a shotgun configuration (both runs paralleled, i.e., connected to either the same or different speaker terminals but with the jumpers in place), and for a biwire configuration (the two runs to separate speaker terminals for the high and low frequency sections of the speaker, with the jumpers removed).
The only physical advantage I've heard in doubling the cable is a decrease in capacitance, which in theory should be a positive but I've no idea if it's enough to be meaningful or if it may have anything to do with the differences I hear in my system.
Doubling the cable in a shotgun (parallel) configuration will cut resistance and inductance in half, which may be marginally beneficial if speaker impedance is low, or if the gauge of the cable is narrow (as it tends to be with many silver cables), or if the length of the cable is long.
Doubling the cable via a biwire configuration will not affect resistance or inductance significantly, everything else being equal, aside perhaps to a minor degree at frequencies that are in the crossover region. What it is alleged to do is to reduce interaction between drivers. Some would also allege that it audibly reduces interaction between high and low frequency currents within the cable. See the paper linked to in the post by Tls49 here, and my subsequent comments on it.
Regarding the specific question, with a 7 foot length of 9 gauge Anti-Cables Level 3, and with most and probably nearly all speakers and amplifiers, while I would not totally rule out the possibility I would not count on either biwiring or shotgunning as being likely to provide any benefit.
Regards,
-- Al