Running different tyres front and back?

So my car is booked in soon to get the wheels refurbed and painted and brought 2 new ps3's to replace the bold contis. Now will it ok to have 2 different tyres on the front so new ps3's and the contis on back? From the reciept the other contis have only done 3k miles so wondering if car will be ok to mix them as dont want to get rid of them as theres loads of tread left.
 
Should be fine.

The general rule is to have the newest tyres on the rear of the car I believe, for a reason I can't remember!
 
iirc you want the new tyres / better grip on the rears to help prevent oversteer events caused by the rears unexpectedly letting go before the fronts.