Here's my contribution to this thread. These are not my line drawings--I scraped them off of the web but did an approximate overlay (pivoting around rear axle location for visual comparison of rear overhang) based on known dimensions, wheelbase difference, tire rolling diameter within 1%, etc. Sorry I used the coupe formats for comparison (even though this thread is about cabs).
I really like the air intake scoops on the Boxster vs the cabrio. The whale butt on the cabrio doesn't bother me. I really do prefer a second trunk instead of an open back seat for storage. I'd like the cab better if the back seat was more of a storage locker, as an option.
Targa is the best shape. The price premium is slightly absurd. Can't really get into it for less than $120k, nearly double a perfectly decent Boxster.