There is no reason to consider or worry about speaker cable length. Here is the why on that...
This article explores if varying the length of speaker cables between speakers really makes a difference in audibility. Watch our related YouTube videos to see what truly matters in speaker cables.
www.audioholics.com
You absolutely do want to consider speaker wire gauge, but you are likely fine with 14 gauge wiring. But, there is reading on this as well...
We discuss speaker wire gauge and how to choose the best audio cables based on your loudspeaker impedance and distance to your amplifier to achieve best performance.
www.audioholics.com
You can use whatever gauge cabling you would like, but it impacts things as the wire gets too thin. Certainly when going through the effort, spending a bit more on the cable will not be the factor that makes it over the top. But, I'd just follow the chart on the link above and call it done. If you already have something like a bunch of 16 gauge cable around, then I would just use that and you are unlikely to be able to hear a difference unless your speakers and room is just absolutely awesome.