2 140 attacks buffed by 10% give a 308 potency attack. A 150 attack buffed by 10% and an unbuffed 140 attack give a 305 potency attack.
There's no reason your true strike shouldn't be buffed by twin snakes too. There's no reason to clip the buff by so much that you use it every cycle, you should be using true strike and impulse drive whilst maintaining the +10% damage buff at all times(fight permitting).