If i was in your shoes i'd keep pushing past Robigrad to Nardona Farma, Connor City and Kalemegdan even. Use the troops for Najran you pulled out to do this.
Materially this does do much damage but psychologically it puts doubt in his mind as to what your doing. In essence your bluffing a position of strength. It might throw him off balance, it might not but i think its worth the risk.
Disclaimer - I'm dead in this game so what would i know
