no tuner is going to push these engines to that limit to find out.
I think United Motorsports would disagree haha. Not to say they have a car and are actively looking for a breaking point, but they've tuned most of the CTS BOSS kits and all IROZ kits AFAIK, including more than a few that are making more than APR 3+ power on a totally stock block.
"Safe" is a moving target, that's the issue. One car to the next and you're not going to have the same outcome all other things being equal. So you set your goal, understand your risks, and cross your fingers. A good custom tuner will know to do things like soften boost onset as hard peak torque hits bend rods, limit torque targets to the currently accepted max, and give you all they can with the fueling you have available. That's the best you can ask for.