I'm with Scotty. If you want to go super low stick with 25mm front, 20mm in the rear.
I saw you were going with Tanabe DF210 springs in another thread. If thats all the lower you are going and you stretch tires, you could pull off 20mm up front and 10mm out back.
I have another option for you........
I also read you like older imprt cars from the early 80's. I sell custom built deep dish steelies in offset incraments of 6mm or so. I can get you 15x8" steel wheels in low offsets.
Here are a couple pics of the steelies on my xb. I'm running with a 2.25" drop on Tanabe DF210 springs. The wheels are 18mm offset up front, 5mm offset in the rear. I ran stock 185 tires stretched on and never once rubbed.
http://www.clubxb.com/forums/f5/3322-pics-rain-downtown-st-paul-mn/