Depends on the tune, the year of the car, the engine model, the VF turbo in question, the type of fuel, supporting mods (intercooler, exhaust mods, fuel mods, tuning method, etc)
What he said. Generally speaking, since we have gotten very little info to support an answer, i'd ballpark 10-20psi as acceptable.
Pull the wastegate line off and find out. I've seen an engine run up to 60psi on the street being driven on a day.
Without more info on your current setup and mods we really can't give you an accurate answer. Just to give you an idea though, my '02 has a stock block/internals with a VF34 and Grimmspeed EBCS and a host of supporting intake, exhaust, and fuel mods with an e85 tune and it's peaking at about 19 psi, but I personally wouldn't want to go above that. When I was running stock boost control (and a few less mods) I was limited to about 15 psi because the boost wouldn't hold steady past that point. I know everyone here likes to give smart-ass sarcastic answers for generic questions like this (and that's really half the fun of being here), but if you can provide more details about your setup you will get the answers you're looking for.
