Just to add the G4S/+/RS chassis seem to just be better suited for use of higher/harder shore tyres.
At all the national events i ran last year i found i always got my G4S working better and more consistent running using 40f/40r or 42f/40r and in some cases 38f/40r.
On occasions that i tried softer rears i always found the rear to slide a lot more.
Im sure setup contributes to this and other factors.
I always have to dial out steering on my dual rate as teh car generates so much steering.