There is some huge debates on this. But wiring is a tricky thing. Especially, when your dealing with frequencies. I've heard and read most of the debates over how the length of the cable and location of your antennae is very or not very important. The only thing I can tell you, is to get two pairs of coaxes, and a SWR meter, and test the difference. I keep forgetting to check into this myself, but once I set things up, I hate messing with them later, until there is a issue. And so far my 18' of cable coiled up behind the back panel behind my seat hasn't caused any issues. But I'm not pushing any power outside of factory settings.
There is also 3 or more levels of coax too!!