I would strongly suggest Improved Sap with your combat build. It gives you more versatility in instances where extra CC is always needed. I'm specced fully into combat with 7 pts in Sub for Improved Sap. While it does effect your DPS if you were to get Improved Sap, it is not enough to make you feel gimped out in the DPS department as I am always still at or near the top in the damage meters. I say go for it.