There is a guy in Finnland who commercially prepares 745 turbo. He gets up to 500hp out of the standart engine. M6 engines where put into E23 where the turbo had no room (right hand steering) Alpina UK build 12 with twin turbo (B10). Equip this one with adjustable turbopressure and you possbly get another 100 hp out of the engine. 200 mile per hour is feasonable. And petrol consumption meassured in "gallons per mile"