I've tried many staggered tire combinations on this car.
245/275 stock
275/305 RE-11
275/315 NT-01
315/345 V710 - For the extreme guys
On all the setups I've dialed the car in to feel pretty balanced, but front tire wear is twice that of the rear. I'm considering a square setup next to see how that goes for front tire wear.
As far as understeer goes on track it can often be driver induced, such as trying to combine too much turning and acceleration. With Auto-X it's inevitable, you just have to manage it.