Originally Posted by aajami
As SamS points out:
I wouldn't suggest using past figures to calculate development the E9X cars were built before BMW's massive environmental testing facility which means these cars are seeing less street time during development.
Also, M is working with AG closer to the start of development rather the completion point so M cars can come to market sooner, like AMG. The F80 is rumored to nearly be complete and many of those parts just needed minor tweaks to work with the F82 (Styling and sheet metal aside).