It boils down to flow, basically. If you can increase the flow by using the same amount of tubing, but splitting the flow path into two lines, you will create a coil that is cooler by removing heat from the coil faster. The cooler the entire coil is, the faster your wort will chill. This is only assuming that the 50' foot coil is restricting the flow so much that by the time the cooling water reaches the end of the coil, its at the temperature of the wort. If this new configuration increases the flow rate through the chiller, you should notice that the temperature of the cooling water leaving the chiller is much cooler than the wort.
Flow rate is dependent on restirction. If you can decrease the restrictio, you can increase the flow. But, the avaible flow for the chiller is largely dependant on where in the house the spigot is located. At my house, every faucet has different flow rates because of location. Your best bet is to build a water tower 115 feet high so you can acheive 50 psi at your chiller, and be absolutely certain that the temperature of the cooling water leaving the chiller is well below the temp of wort. <----for reference only... dont quote me on these numbers. (But, 50psi / 0.43333psi/ft_elevation = 115.4ft)