Congrats on the OSG and AST setup with M3 bits. *sigh*
I want the same thing for my e90. Got the Quaife from Harold back in the day when it was the only game in town (pre-Wavetrac) and OSG was soooo expensive...as I recall.
I was in a hurry to install a real diff that met my needs at the time, while reducing the wear and tear of the brakes induced by the nanny controls that passed as e-diffs for our rides.
Looking at the 400/800 Swift Spring setup with the AST singles, though... currently have 219M wheels and the potholes are not as severe in the Mid-Atlantic...
Can't wait to read your review/impressions once you put on your new toys!