I ran 12psi on stock turbo for over a year without any issues, but I know others that havent been so lucky, I'd stick to 11psi.
Its not un-safe to be running 10.5:1 AFR's, quite the opposite really (unless hes checked a bunch of timing at it)
See where your power starts to drop and notice that its also where your AFR jumps to 10.5:1 This is where you will be losing your peak power unless you have exhaust/intake restrictions or some other kind of issue. How does the plot for your boost look? (If they gave you a power vs boost graph)
If not and you want to know, the dyno run should be stored in there dynos computer and you will be able to go back and get them to print one out (assuming the plotted the boost, which they should have)