I dropped my car with H&R Supersports. It is probably ~1-3/4" in the front and ~1-1/2 in the rear. But bare in mind that I replaced my rubber isolators with urethane isolaters and I lost a 1/4" on my drop. My MM C/C plates can barely get me back in spec. As much as I love the look I think it's a little rough for a daily driver. I may swap out my Supersports for some H&R Race springs. I'll loose about a 1/2" of my drop but it's better than going back to 4x4.
In answer to your question. Anything more than a 1-1/2" drop is going to be questionable for C/C plates.
I still like having my MM C/C plates over the stock plates for the adjustibility that comes with them.