toedder:  there are various MET (Match Equity Tables).  gnubg--and any other capable playing software--should let you specify which MET you want to use for cube decisions.  The MET are tables showing the theoretically expected match winning percentages from various match scores...assuming equal-strength opponents.

The MET are less important at scores such as your 17 away / 16 away.  But I'm currently trying to memorize those values out to about 7 away / 7 away for real-life tournament play.