Casber2311,

The question is too broad to have a pressure limit for mold breakage. You should only use the minimum amount of pack pressure needed to pack your parts (until there's no more distortion or sink). In a perfect world the tool-steel should be adjusted to satisfy the correct dimensions when part is fully packed and process is capable.

I would almost never rely on a mold-flow simulation to determine pack pressure.

Try opening up your gates (increasing flow) so you can pack your parts with less machine pressure