Do you have an XI?
Any plans to drop the car? And as ACEE mentioned it also depends on your tire sizes as well.
But just from seeing other pre-lci's with agressive fitments I have seen et's as low as 20 in the front with a 8/8.5 inch wide rims and et's as low as 20 in the rear with 9/9.5 inch wide rims.
Taking the dimensions that ACEE gave earlier you could go do 12mm spacer in the fron (which would give you an et of 25) and a 15mm spacer in the rear (to give you an et of 24). The wheels should sit pretty flush at that point.