Your biggest problem when you turn up the boost on the smaller turbo's is the intercooler heat soaking. The T25 or 14B "above" 17 psi heat soak bad on the stock intercooler. If you upgrade the intercooler you can run upwards of 20 psi without any loss in power. If you are making back to back runs at the drag strip, try spraying the intercooler down with a water hose in between runs. Running water, alcohol, or methanol injection will help tremendously.

On my stock 7 bolt 4G63, I personally ran 21 psi on a big16G and pump gas with all the supporting mods. On race gas I ran 25 psi. Unfortunately on a fwd car with 330whp on pump gas, you spin everywhere you go.

When I was on a 14B, I couldn't make anymore power running above 18 psi with my supporting mods. 20 psi would just heat soak the intercooler and yield slower times.