Steve-
First, a wire of any reasonable size can carry several hundred amps if shorted out, and result in a fire very quickly. For this reason, authorities reccommend:
1) The cable should be connected to the battery switch, not the battery. Otherwise, the cable up to the circuit breaker on the helm panel would be live at all times.
2) A fuse or circuit breaker should be installed close to the switch for further protection. Since the 600 draws 50 amps at full (calculated) load, an 80 amp fuse/breaker should handle the surges and still provide overload protection.
Secondly, the wire gauge problem is really more one of voltage drop to the motor of the windlass, and less one of heat build up in the wire, as actual use is intermittent and/or infrequent. The voltage drop causes the motor to use excessive amperage, which results in a greater percentage of the energy turning into heat in the motor windings. Too much heat and the solder on the commutator turns quickly into an order for a replacement armature.
There's a nice full page discussion in the West Marine Catalogue (page 660 of the 2004 edition) regarding wire and current loading with tables and a formula for calculating the voltage drop.
With the 25 foot or so round trip from the switch to the motor and back, the chart says to use 2 gauge for totally adequate service, but 2 gauge is full sized automotive battery cable, and seems awfully big at first consideration. Too big to install easily. Too big to look good. Too big to hide. Too much weight. Too much Too much!!!(?)
So I went back to the table and figured how much I thought I could safely downsize. 4 gauge would be ok, maybe even 6, considering the intermittent use and my not planning on using the windlass as a brutal winch to haul up sunken logs, abandoned Bayliners, etc. (It would be interesting to put a ammeter in the circuit and see how the load goes as the windlass is used....probably pulls 20-35 amps most of the time.)
So I went with 6 gauge, and haven't had any problems yet. My Quick Aires pulls 500 watts (42 amps, not 50, calculated, as with the Sprint and Horizon 600's), and I've never opened the circuit breaker. I converted over to 100 feet of 1/4" chain (74 lbs) plus 150 feet of three strand nylon rode, and the extra weight encountered there hasn't been a problem.
One way of dressing up the installation in the V-berth is to use duplex wire from the solenoid forward instead of the individual red and black cables. The double wires are spiral wrapped with a cloth tape then covered with an off-white plastic sheath that hides much better against the v-berth walls. Alternately, you could also just wrap the individual pair with white electrical tape, as the 6 gauge duplex is $5.29 a foot at WM. Incidently, the various types of cable can be purchased new at about half West Marine cost from vaious sources on ebay.
That's about it for now, was nice meeting you and your folks at Lake Shasta. Joe.