Firstly, well done for being in such a position.
If this is being run through a company, aren't you responsible for CC tax? If so, most "interesting" stuff is surely ruled out? Even ignoring the tax aspect, you must be spending a fortune on fuel.
If CC Tax is an issue, then the clear choices are either a 123d or an Alpina D3S, even if CC Tax isn't an issue, these cars still make a compelling fuel economy argument for themselves when compared to a 325d, 330d or 335d.
I would be inclined to suggest that a 2.0 diesel beemer will save you enough in fuel to be able to buy a 172 for track action, though you would probably be better putting that away as a deposit for a house.