Remember that Big-Phil comletely blew up his old engine with one detonation instance at 20PSI.
In engineering we have what is caled a "safety factor".
It is the amount of stress that a part was designed to safely undergo without failure divided by the amount of stress that causes failure.
When you up the boost you are reducing your safety factor closer and closer to the number one.(bad)
With less of safety factor available even the least amount of detonation can can sen you under the number one and give you a basket case of a motor.
"Safely" I would use no more than 14-16 PSI on a stock, unopened, 75k-150k mile motor with a stock-ish turbo WITH an intercooler...depending on your mods.
Big-Phil's nice "stock" motor is FRESH with new rings and bearings, etc... so he can have a little more freedom with "fun" things like more boost etc...
Just my 2 cents...