ptv seems easier and better for resale. I only saw one person put a pure LSD in the GT4. That said, I have no idea what the perf difference would be. I would ask on the GT4 forums. I certainly spec'd mine with PTV to avoid hacking it up.

 

A LSD is going to allow you to get on the power sooner on corner exit. It makes for faster lap times. Also depending on the LSD ramping you will have more stability under braking (less tail wag).