I would encourage you to cut the log into two logs, primarily due to yield loss.
Lumber yield from a log is typically determined by the small end diameter of the log. If you cut the 17 footer into a pair of 8'6" logs, odds are that one log will have a larger small end diameter and yield more material.
From your comments about only having ray fleck visible in part of the board it sounds as if you are not centering the pith on the the log before making your opening cuts. When quartersawing, if you don't center pith on both planes you will produce boards with fleck only on one end of the board.
To center the pith, simply raise your toe boards or wedge the small end of the log away from the deck until you have the same distance from the pith to your blade on each end of the log.