It is difficult to compare. The cell is 70g heavy, capacity is 2,3Ah and voltage is 2,6V (empty under the load).
The 4Ah lipo has end voltage 3V and weight 100g.
So if I compare the w/g capacity, I am in ratio (4 * 3 / 100) : (2,3 * 2,6 / 70) = 120 : 85 = 1.4
Means lipo can keep 1.4 time more capacity in the same weight. But A123 can be drained more than 90% of its capacity, while lipo only less than 75%, what makes that number little better: 1.4 * 75 / 90 = ~1.2 ... means A123 is in any case 20% heavier. So yes, more wiring and, longer cables and so will meake 100g more than lipo.
Unfortunatelly it is not whole story, other problem is that they make only one size 2,3 Ah. 8 cells 4s2p is too heavy and too little voltage, too high current, too slow charging. Usefull combination is 6s1p and that is not enough capacity for 12x6 prop (with motors I know). Usefull prop is 11x5.5 and that needs smaller plane. I would say under 1500g, or even better 1400g and if I count well, 450g battery, 200g motor, 50g esc and battery protection makes 700g ... means the power train must be half of the whole model or by other words, the trimmed airframe with landing gears and all hardware must be at 700-800g. My lightest airframes (for IC engines) are at 900-1000g.
So I see two chances, I either fing better motor with 10% better efficiency (and that looks difficult) or I just must build lighter model ... I prefere the first choice, because I have two such planes with exchangeable motor.