I wold say better to have Tyres with most tread on the front driven wheels, especially with winter coming and with standing water they hit puddles 1st.
I just had my new tyres on front and left the rears as they were, they also have 6mm on rears although are cheapo tyres on rear, once they wear out a bit more i will put some Toyo T1R on the rear to match the fronts, can't go wrong with T1R, been using them for 5 years.