I am using the sound king 10 gauge speaker
cable. would there be any increased performance
if I used both the + and - cables together for just
the positive or negative?
By shorting 1 10AWG cable to use as the (+) and one for the (-), essentially doubling up on your wire, you lower the effective gauge by 3AWG. Thus your 10AWG speaker cable will now become 7AWG. This does lower resistance considerably, but 10AWG wire is already low to begin with. If your runs are less than 50ft or so, its mostly a wash.
The downside of doing what you propose is you will now double your capacitance and possibly increase your inductance if you don't keep the conductors closely spaced. I personally don't think its worth the effort.
You would yield more significant sonic results by better optimizing your room acoustics and speaker placement.