It's kind of nice that Greddy teamed up with Garrett. I think they make some good turbos. I'm currently using the GTX2867R and she purrs
The T518z is capable of 14PSI with the current actuator installed. If you have the time to upgrade the actuator on the T518z it should be capable of around 18PSI. This was information I received from Andrew at Greddy USA.
The link below is the actuator someone can use on the T518z. However, some modification will be required.
http://www.shopgreddy.com/turbocharg...17z-turbo.html