Half-iced, right?
I always drove with four until I hit the monster rock that I thought was just a soft clump of slush.
I never had steering problems with my performance tires on, but in the snow and ice, the back end would break free all the time, even in consistent speed.
If your choice is between two and none, I say put two on the back. But four is much better. I also say don't take it out in the snow with only the performance tires. Too dangerous. The penalty is too high.