Lowering Springs....?

[Jay.Blanket]

So i have tried to look back and search though the forum because I am certain this question would have been asked before.....

At what point of lowering a Standard AU Falcon (AUII in my case) would you recommend replacing the shocks and springs?

I have just picked up a set of SSL rear king springs cheap and want to know what would be the best height for the front? should i just find some SSL fronts to go with it? also should i replace the shocks?