RE: 2s and 3s a123 cells in my traxxas rustler and stampede
Any esc can handle 2s1p or 2s2p a123. The voltage is 7.2 max, with 6.6 being the average during the discharge cycle. Voltage is lower so the motor turns slower. You may want to get a faster motor or gear your motor with a larger pinion if it can handle it. You don't need to set the esc to handle anything - voltage cutoff isn't too critical with a123. Just stop when the car slows down.
In my rustler I run a mamba max 4600 with 13/87 gearing using 3s a123.