Even with Ares V, I doubted if cassini will use it. The reason is that, although it takes shorter time to get there, a lot more fuel is needed to send Ares V or Saturn V like rockets to the space. It is not efficient. The best way is to have space station like middle hop, and launch the spacecraft to the middle hop and get refuel. Most of the fuel currently is used up in the first stage. Bigger the rocket, heavier it is, and more fuel for the first stage is needed.

I have not done the computation myself to determine whether Saturn V is enough or not. That is in fact, very complicated. Because that involves finding the orbits, and working out the orbit maneuver. That is not a simple task.

It can't be done by simply taking the E=mv^2/2 approach. The reason is that, the Saturn V is 3 stage rocket, different stage has different thrust and burn time. To push something to Saturn orbit, it requires a lot of intermediate orbit transfer, and have to find the right spot to initiate the burn. Hence with the limitation of the number of burns and staging, it may not be possible to push cassini to the mission orbit.