4.6is was sold in 2002-2003 in North America. So you would be comparing a 2002-2003 to a 2005. Sounds like you should go with the 05 as it is a newer and near last of the E53 platform so should have most of the bugs worked out by then. 4.6is are also very hard to find.

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2003 4.6is - SOLD
2003 M5 Imola
2008 Mini Cooper S
2011 Mazda CX9