I tried to find a flow map on them, but Z1 doesn't have any on their site from what I see, and I don't know what Garrett turbo they're based on, either. But, based on what Z1 says in the description about the turbos, I think 18 psi is going to be about the peak efficiency. Of course, you can always try going higher since you do have the wideband and nistune. But I personally would feel safer if I had exhaust gas temp readings to go along with the wideband if you're looking to really push the turbos. Either way, be careful :)
