As far as the 350z goes- it is truly a beautifully engineered vehicle. I have test-driven and rented many different higher-end vehicles, and so far haven't driven one in the 40k-80k sports range that I prefer. The Shelby is beautiful, and roars when it needs to, but it doesn't have anywhere near the quickness or turning capability as the Z. As far as Audi's- they are also very well engineered, but I just haven't seen enough emphasis put on them in the business community. Mercedes still rules the court. Every multi-millionaire that I have met or have done business with owns at least one Mercedes. Then again, they have all given me positive feedback on my Z. I am younger than the majority of them (all of them, actually), and it is expected of me to have a more 'fun' vehicle. All of them have children and families, and can't always get away with having a two-seater. (One of them owns a CLS AMG, and mentioned to me that he is talking to his wife about getting a Z after driving mine). If I was driving around in an ML, GL, or X5, then I'd look like I was trying to be just like them! By driving something a little different, I emphasize some of the good things about being of a more 'fresh' vintage, lol.
Once again, my recommendation for an SUV is the GL series. As far as sedans, there are plenty of them out there to choose from. All of your selections have been good so far, so go with what fits you. Uniformity is never the answer. Don't be afraid to choose a vehicle that is typically not associated with the corporate world, and don't let today's 'business-chic' fashions dictate what you drive.