The only problem I have seen with the SmartTrack (curve, not A-B) pattern when using an OnTrac 2 is that any little wiggle in your line will get amplified each time you make a pass.  Each consecutive pass, the OnTrac2 tries to follow that little wiggle and it progressively gets worse.  With RTK and hydraulic steering however, I have not noticed this.  The guess rows should not be any different between smartpath and a-b, other than what I just mentioned.