Over here, there are a some guys running well north of 130cv with boost manually set to 1,2Bar. I don't think it is unsafe per se... They mostly do short drags (250mts). I think it mostly has to do with how much abuse a car is expected to take in.
I don't particularly like that guide at all. We should write our own, Uber
The EDC15C calculates the combustion temperature if I'm not mistaken and will try to limit it, that is if you don't screw it up by altering any of the injector callibration tables!
Short runs are okay with 6 bar of boost pressure, by definition, but pushing a car on a highway for 20 minutes at that isn't very advisable. Use adiabatic compression calculator and then compare the net stored energy after fuel add vs. the unmodified engine.
EDIT: I listed some beginning points here, for example:post55395#p55395