With the weight of the car resting on a jackstand under the control arm, not much short of the epicenter of a big earthquake is going to knock it off. If the jack supporting the control arm looses pressure or slides out you're going to be in deep yogurt. Jackstands don't have wheels!!! Jacks should only be used to lift a car. For any underneath work jackstands must be used, and I would NEVER,EVER rely on a jack to keep a spring compressed while I'm there doing any work.

Think about this for a minute and decide for yourself which procedure is safer.

One other suggestion. Jack the whole car up and support the rear at the rear rocker panel lift pads. It's best to have the car level rather than just having the front end up on stands under the control arm. The more nose up the car's attitude the less weight is on the front to keep the spring compressed as much as possible.

Duke