The width of a PCB trace is only about current, not power. Voltage is important only to determine how far one trace is from another trace, pad or other conductive object.
As for power dissipated by the trace. If your 1.28 mil wide trace was 64 inches long, and you put 5 volts to the ends, your trace would dissipate about 1 watt. (1)
Realistically, a 1.28 mill trace width is to small to be practical with standard processes. Most board shops want 6-8 mils minimum.
Note 1. Assuming that the trace stayed at 25C.