Even on an open track like as4/as5 the UFR beats Xfr with nearly a 1s a lap. So the thing with long straight road to gain something with Xfr over Ufr aint true, that is if u look on wr laps.
And on NEC championship with these cars Ufr had somewhat 15kg on Ky3 and imo that killed it even in the hands of Troy and Eisboer.
Gl to make them two NGT´s somewhat even against one and another, just leave the Xfr alone and focus to slow down the Ufr.
:P