The shop owner said that the reason hp didn't keep climbing at high boost near redline(like the low boost run) maybe because the valve springs are weak, and couldn't keep up with the cylinder pressure. I said that the turbos might not be efficient at that psi but he still seems to think that with stronger valve springs, it will do better. But I can't argue with the guy who build 7s mustang with this:
1990 300ZXTT Twin Greddy TD06L2-20G (No Nitrous) 822rwhp 694rwtq @ 31psi Best et/mph :10.56 / 142.47mph