I bought some 19" E53 wheels (72.5mm hub) for my E70 (74.1mm hub) back in April 2011. The seller is a racer and directed me to a machine shop that bored out the wheels to fit. I thought of doing it myself, but am glad I spent the money to have it done correctly. The ride, balance and alignment are perfect and I have had no problems.

There are some other threads on this topic and someone suggested that the step down spacers are not as safe due to sheer forces.