How many scratches you got to fill? I started with Z-5 around 30k miles, had been using carnuba up to then. Z-5 worked great.
Ran out around 55k miles, Z-5 pro is what I got this time. I got 'there' with four coats of Z-5 pro (Z-5p, Z-5p, Z-2p, Z-5p, Z-5p and 1 coat of 50-50 Z-2p/Z-5p) and since then two coats of Z-2p. I was expecting to use 6 coats of regular Z-5, so the pro saved me a little time, but not much.
If you got more than 40, maybe 45k miles on the car go ahead sell your Z-5 and start with the Z-5pro. Otherwise I agree with the others, use up the Z-5 and get the Z-5pro next time.
FWIW I am very happy having used up my Z-6 and having switched to Z-8 exclusively. Ten bucks, yeah it was worth it.