M57 Technical Specs
Here is the document that entails all the differences between the Euro and US version and E70/E90 differences.
Overall summary - US versions have a stricter emissions system. E70 comes with a low and high pressure EGR system. Where the E90 has only high pressure EGR system. So it is stricter emissions for the E70.
I can't imagine E70 with high miles with the old EGR system not having carbon build up issues, as BMW also released the update for them. The cases are probably just not documented on the internet.