Mark, cut it long if you can so checks on the ends can be cut off when it is cured. Are you planning to make a bow from the pole or two bows? What specie is your dogwood?
WVFK, the butt log(4"dia) had about 30deg twist in a 6' pole. It had been an understory tree so it was tall and straight. Other under story trees, around here, like sassafras can have 90deg or more in 6'. There in a sourwood tree near my deer feeder that has 3 complete twists(3x180deg) in about 10".
Pat