Well I must be doing something wrong because I am using a 40 amp fuse for 2 amps with 60 amp fuses and have had no problems? with 4 gauge wire from front to back, 0 gauge wire is over kill and is only for serious competition systems running sreious bass.
If you ain't poppin that 40 amp fuse that simply means you haven't pushed much over 500 watts..... yet, but I agree with you about the wire. 4 gauge should be fine for most "daily drivers" if the alternator is up to snuff.
16 ft of 4 gauge at 65 amps corresponds to about a .3 voltage drop. That small of a voltage loss would probably be insignificant in most cases except maybe when running your system with the engine off.
Regardless, unless you're running 8 gauge or something there's no reason why you can't run a fuse at the battery slightly larger than what your amps are rated for. That fuse is there to protect your wiring and car in case of a short, not your amplifiers.