The Covert Revolt and Sigma Sting are both strong balls. But both would be a better option to reduce the over/under you are seeing.
If you are looking at the current lineup, I would start with the Venom Toxin and then go to the Rage when it starts to burn up. If you still want something strong, then I feel the Revolt would be a good ball to start with and give you a good separation between the two balls.
I am different than a lot of people where I like to have a weaker solid/hybrid then transition to stronger pearls when they begin to hook early. When I have to move left, I want to make sure the ball I have is strong enough to turn the corner. I have tried it the other way around (strong solid and weaker pearl) and I end up with a situation where my speed starts to be a detriment.