I had a deal on an exact car like yours to trade with my 09' 650 cabrio with 64k miles. I didnt do it because that m6 didnt come with warranty. I think u better fine one. Its an amazing beast but I heard from people maintenance and warranty out of your pocket is somehow not favorable.
2009 BMW 650i Cabrio (daily drive)
2011 Audi A4 (groceries, bully, road trip, winter beater, family car)
BMW CCA ID: 473647