That turbo should do 330 on 93 nd no meth averge hp on 20 psi. You should be able to rise that by 30 hp pretty easy with meth and timing alone on 20 psi. Add another 30 with some more boost and yea, your knocking on 400 on that dyno.
If your spraying to much meth your already killing your numbers on that pull.
You could always just throw some more boost on what you have now and keep your fingers crossed