I would use no less than 4 gauge to the amps. I've also used a short run 4 in from batt / two 4 out to amps many times with no adverse effects. In fact may current system running a Harpoon & ZX700.5 was wired that way and has plenty of power (until i gutted the entire system three weeks ago). What looks good on paper doesn't always reflect real world results.

Quality wire and cable is also important and as said KnuKonceptz is the best online source i've found. Been ordering from them for four years now and it's quality stuff.