It seems Dinan holds their sale (if they have one) the last quarter of the year. So September-October, but I don't have confirmation on that. Just our experience as a dealer.
I posted this a couple days ago. Doesn't help if you aren't in the Bay Area.
http://f10.5post.com/forums/showthread.php?t=701412
My 550i M Sport is another beast with the Stage 3 and exhaust. It is a night and day difference compared to stock.