btw back on topic, the 50 more armor of the centaur will allow it to survive a medium tank much more easily as it will have the same armor as a Sherman (and before u say ostwind can outrun other tanks, it's slower than all other medium tanks)
The speed is helpful for escaping range of any unit, including mediums. You don't need to outrun the tank, it's not Nascar. You just need to get back close enough to your own units to scare medium away
The p4 has about a 2/3 chance of penetrating it, everything above that is still guaranteed