I think I am correct in saying, that the starter pack will give as much as the car draws, up to its limit. A little bit dead battery will not draw as much as a very dead battery. It doesn't shoot into the dead battery, so much as get sucked by it.
I would say a good indication if the genny is capable of starting would be the thickness of the leads. If they are heavy, like a starter pack, then it is possible that is what it is designed for. However, if they are thin, like a charger, then unless there is some kind of built in protection, they may just get hot if you try to start the engine with it attached.