A stock E55 (like my 2003) should be a little faster in a straight line, but not by much-after all it's a 4100lb pig.
Having said that, I'm planning on trading "up" to an E90 M3. It think it's the best overall car on the market. After 6 years in the E55, I'm missing the 6sp manual, fold down rear seats and track worthy handling.
Both are great cars, but the M3 rules IMO.