Glad to see someone else has experienced the same as me.
Falkens are just too soft for a heavy car such as the Z if your pushing the car in any way. I've been waiting for camskill to get bridgestones back in stock for the Z fitment, as I just can't get on with the falkens. Everyone who raves about them in the stock sizes and profile must just pootle about everywhere and prefer comfort over performance.
Also, the whole mixed tyre thing is over exagerated on here like someone else said above.. Different tyres on the same axle, yes, its a no no especially on a RWD car. But mixing tyres front and rear is made out like its instant death for people on here..