If you do a lot of straight line racing, you bought the wrong car. The Boxster was not made to go fast in a straight line, but it can outrun most cars on anything twisty. Unless you do a $10k 3.4 swap the Boxster will not make you competitive with the cars you mention in a straight line. But if you love your current Boxster this is the way to go, and the way I would do it.
A 987 may not get you the HP your after, but would give the same/better handling as your 986. I think my first choice in your situation would be a 996/997, there fast and will handle similarly to the Boxster.
Then the Viper. I would have a problem spending $45k on a Dodge too. But I will admit, I have always liked the way the Viper looked. Plus, you rarely see them anymore which in my opinion makes one 10x better than a vette.
