Try Search Tab, on this site...lots of info.
Here is a thread link detailing wheel sizes:
http://www.xoutpost.com/bmw-sav-foru...omparison.html
From fading memory, I seem to recall some posters suggesting they did put the bigger bore size E70 wheels on an E53, using hubcentric rings.
As for E53 wheels on an E70, some other posters have had success with a simple machining process to enlarge the E53 wheel hub bore to E70 size.
Ebay is not exactly the encyclopedia of knowledgeable 'informed sellers'.
GL, mD