I think in a softer wood that you should not need more than one bit. I have a 3/4 straight bit that I have plowed many, many dados in MDF, which is much more damaging to bits, and it still cuts very well. Keep a steady feed rate, keep the bit free of pitch, and give it a quick touch-up with your hone when your cut starts to bog down and you should be OK. Remember heat is the enemy, give your bit and your router a chance to cool off.