[ZDan]

PSM for sure has to be turned off for trackwork with the 987 in the dry, so *if* it includes an e-diff feature I'm sure it gets turned off with PSM. In treacherous wet conditions, however, PSM is *very* good.

A serious track build on Hoosiers or other uber-grippy tires will almost certainly require a limited slip, but an aftermarket unit is a better bet than the dinky optional Porsche LSD. Which apparently wears to the point that it's essentially open after some number of track days anyway.

For street car on streetish tires and suspension, I'd say LSD not required.
*IF* I get another Cayman for street/track, LSD won't be a requirement for me, which opens up the available cars IMMENSELY!