That is so interesting. From that information, you might have a working theory that George Powers was actually of the Bennett line (father) and William's father was a Cook. Were there any Cooks living close to the Powers in Smyth Co? If so, you have more names to work with. I found in court records a William Cook, Jr. in 1825 (Wythe) was appointed guardian for Samuel Crawford; in 1832 a William Cook, age 70 was declared a Rev War soldier; in Smyth Co there was a Robert Cook attending a sale which also included a Shupe in 1842. This would have been more toward the southern end of the county. The 1840 Smyth Co Census lists a John Cook, age 30-40. Looks like you have more digging to do.