I think its actually the 4liter(4398 M62)thats been re worked by M thats why you cant get a hole lot out of the engine with Normal mods(porting the heads re boring) unless you spend big because its nearly at its limit of releiability the only "true 5liter are the 5379 M73 V12 in the E38 7 series and the 5576 S70 V12 in the E31 850csi even the E60 M5 isnt 5liters 4999 but imagine that, an E39 Touring or saloon with an proper M tuned V12