I've heard 1 bar, 1.1, 1.3 being the max on the stock ceramic turbos. Ceramics do spool quicker but can shatter under extreme heat conditions or during some particularly nasty detonation in the exhaust tract, like that anti-lag that WRC cars use. I think the Japanese think 1.3 is the max on stock ceramics, but then again they have better gas over there. Did you remap your car for your local gas? I think it's avoiding detonation that's the main thing.
btw, if you do blow a turbo, pray that your foot is on the gas, and the bits will shoot out the tailpipe. If you lift right when it shatters, the vacuum will suck the bits into your intake, which I think is not so good.
AFAIK, there is no way to tell without actually taking a visual look at the turbine inside the housing. You don't have to disassemble the turbo, just the intake pipes so you can take a look at the innards.