http://www.bombaydigital.com/boxster/projects/trailer/
IMHO, the Boxster is not the tool for the job you're trying to accomplish (i.e., carrying things). The price differential between your Boxster and the other options you mentioned would easily cover a nice little Subie or pickup to haul stuff around.
If you want to go faster in a straight line, just sell the 986 and get something with a bigger engine (i.e., 986S
).
First, you should figure out what you really want...