Here's the E46 strut brace on my non-M Z - it's about 15-20mm out either end. Aret the strut towers further apart on the M Zed?:
M3 Strut Brace 1.jpgM3 Strut Brace 2.jpg
and here's what I replaced it with on the M3 (which was a noticeable improvement - the OEM strut brace is purely for show IMHO):
M3 Strut Brace Aftermarket.jpg