Max boost from a 1.8t k series??

I have a ZR with the 1.8t from a Rover 75 fitted and I have the Z&F map. I've had to remove my boost solenoid and run the pipe from the boost outlet directly to the actuator. I'm not sure what the boost psi is at the moment but it's not very high at all. I have a boost gauge and manual boost controller which I will fit the weekend. My question is how high would I be able to run the boost safely an not have the ignition cut by the over boost protection? If I up the boost do I need to have a retune?

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