Did a direct comparison between the GX and the Moore Speed MPS last sunday on a middle large flowing low to medium grip outdoor asphalt track; both bodies were the lightweight version.
The GX effectivly calms down the rear. So my 6.1 with the same setup changed from aggressive turning to a tamed neutral behaving. I reduced the rear toe to make it turn better. The car now turned better in slow corners and kept its tame behaviour in fast corners.
The laptime comparison is not easy as the track changes during the season. It is in spring around 5 tenth slower than in fall. In fall last year my fastest was a 13.7s/lap. Yesterday I managed several 14.0s/lap with nearly dead tires and 17*C.
So outdoor this body isn't slow at all and makes my car more easy to drive