[SeanWRT]

Congrats for the Cup2 upgrade for free! PSS in my opinion can not handle m2 torque even in its stock form.

Rest assure you'll be fine having just Cup2 on rear. If anything, it's a more planted rear end for you, provided tire operating temperature is reached, which isn't hard to make happen.

No need to worry about understeer when turning at car's limit, because that's a different limit than with PSS. Braking bias isn't effected either, though it's not optimal but is still better than PSS. Take it that it will just grips a little bit more.

Look at it this way - High performance car consumes rear tires much quicker than front ones. And we don't just change 4 tires at the same time. When replacing rear tires, we will have better grip with new tires, either of the same spec or different, anyway.

Though down the road you'll be changing tires much more frequently as Cup2 is much less durable than PSS.