What I have gathered from talking to a few knowledgable people....

It doesnt really matter how stiff each swaybar is, the difference between the front and rear is what will change the most handling characteristics.
eg. no swaybars at all would be comparable to having both stiff ones. Of course the amount of bodyroll and alot of other areas will be different, but the overall handling characterstics and reaction of the car would be comparable between the two setups.

It has alot to do with driving style and what the car is setup for.

I know of a car which we ended up completely removing the rear swaybar, and putting the front on full soft. This was in an a9x torana, so it had no nifty suspension design like modern cars, just coilovers and some adjustable arms....