rs4 rs4v 25gfour etc all seem to have 4.3
rs4s 260rs seem to have 4.1
we had a rs4s rear subframe that we put in our converted car, as far as we can see its identical to our gtr ones (electric hicas etc)
the 260 and the rs4s subframes are narrower than the normal non hicas subframe in the stagea tho, so you will want spacers on the wheels
hope that makes sence