You can upgrade it with a smaller pulley, but just know that it will void whatever warranty VF gives you. I haven't measured yet, but I don't think the pulley is a standard Vortech pulley, so you'll need someone to make one for you. You'll need a tune too, which is the hardest part. I see no issue with bumping it up to 8 psi, especially with water/meth and a good tune. Some people run around at 8.5 psi with no intercooler on ESS Stage 1 twin screw setups with the TS2+ pulley, and those setups should be more prone to detonation because they boost the car more at peak torque.
G Power Z4M
and VF Engineering Z4 3.0i