The GPR drive and feel very smooth, never was too stiff unless you make it and the lap time was very slow for me when you set up stiff.
I dont think you can justify by thinking about it nor seeing it run before
I haven't try the extra rear spoiler yet but the faster guys have them and had a more consistence "sector 3" , which is the straight plus the 180 deg almost full throttle turn, then me. This could be his driving or the wing.