this whole idea that you have to workout until your sore is utter stupidity, it was started by stupid people because it was the only way stupid people could get attention.
Your not looking to be sore, your looking to be fatigued, your muscles shouldn't scream because you scratched your balls, they should feel weak, used, workouted, they should feel like you have done a lot to them, but not sore.
Best way, after workout your chest, sit down in a chair with arms and get comfy for say 20 minutes, then get up, using your arms to help push you outta the chair, if your chest feels tired, ie, you feel some effort in your chest muscles from helping push your self up, but you don't actually feel sore, then you've reached your goal.
If you push beyond that and you feel sore, not just tired, you've gone a little to far. It takes a while to distinguish between the two but when you hit the right fatigue you'll know it because it'll feel right.
anywho, thats the way I think of it and from my own research that's the conclusion I've come too and it seems to be working for me