One thing I am not seeing mentioned, as to proper wire guage, is amp draw. You only need a wire heavy enough to carry the amp draw from the amp. The budget wire may claim 4awg based on the jacket size, but they still have to put the max amp rating along with it. Best way to be safe is to know the max amp rating of your amp(s) based on internal fuse ratings, or as stated by the mfg. and aim above that. Most, I repeat, MOST good quality 4awg wire is rated to 125A at 20' lengths, some oversize and can do 150 at 20'. Above that your looking at 0awg, wich for the most part is good to 300-325A at 15-18'. This is all in pure OFC wire. If you get into CCA wire, it all goes down, eg. oversized CCA 0awg can go up to 20A at 20'. Just incase some didn't know.
2001 Tahoe LT Auto-Ride, 5.3 (Soon to be 408 stroker!!!) Newly rebuilt 4L60E!!