The T1 sizes are not really a hot set up but rather a limiting set up. In fact the 10" front using 315's reduces the 315's effectiveness.
If you are not bound by the T1 rules you can do better.
I recommend:
305/30x18 on 10.5x18 with +0.25" offset for the front and
315/35x17 on 11x17 with +0.25" offset in the rear.
This neutralizes the handling, increases front grip, increases front turn in, decreases braking distance, increases front steering response and modulation, reduces understeer and stabilizes the flex of the front side wall.
It also increases rear traction under hard acceleration and cornering allowing the car to "squat" better.
This results in higher corner entry speeds, mid corner speed and corner exit speed.