Newman Atkinson says:

Power is more of how you wire it. If you are wiring to one point of the tracks the farther you get from the power supply the more power loss you will get. If going through several switches power loss is definently noticeable. It doesn’t matter whether you run on standard DC or go to the new DCC. The farther you get from the supply the worse you get. You loose power through each track connector in the rails You will see this in standard DC as the train slows down on tracks farther away from the transformer. Wire buss wires under your tracks, 16 gauge or better Basically trailer wire. One wire for each rail. every 4 to 8 feet use wire drops (connections to your rails above) down to those main buss wires this keeps good power to your rails all the way around. These are usually very short and phone wire is plenty good enough for those short distances from the wire buss. (those are usually 22 or 24 gauge wire for phones. Someday you will want to convert to the new DCC system and power drop is your enemy.
You loose too much power you will loose control or signal to your engines. So wire with the wire bus system and your layout will be nearly ready to change to DCC later. from Newman