Thanks for all the replies. I thought I just try it myself and bought the lightweight body.
I compared the body form with the HotBodies Mazda 6 MooreSpeed MPS and found the form to be the same except of the "sharper" edges and shorter nose (therefore longer splitter) on the GX. So maybe these two will be close. For me the HB Mazda6 MPS was clearly one tenth faster than the PF LTC-R on my outdoor track (amsc-augsburg.de). Test drive will follow later.
Right now I am just happy about the look: