Go and test drive it and don't worry about the engine size the 2.0d engines are magic you don't have the tone of a inline 6 but you will get to love the noise of that turbo spooling up
that 2009 version came out with a 130kw / 400nm engine iirc. should be more than sufficient for that 5 series. It wont be as quick as a 3.0d, but should be more than enough to keep you happy.