I don't know if there is an actual published limit. I do know they are almost as many grams of glass as mL of beer. So with that said they're fairly strong. The only other bottles that meet or exceed that ratio are champagne and other specialty belgian bottles. You have to remember that most import bottles are stronger than domestic bottles because of the long ship ride they make. The containers are all treated the same so they spend more on bottles to not lose product.
What carb level are you looking for bottling in these? I would assume they can take 5 volumes safely. Beyond that you're bottling champange and I bet something would give at that kind of PSI in the bottle. I do not believe there is a formally agreed upon upper limit for these bottles. Just live comfortably they'll take up to 5 most likely. I would still play it safe and put the bottles somewhere easy to clean up and or protective when dealing with those pressures. If you're just looking to do between 3 and 4 vol for something like a high carbed saison, you're fine, I do that all the time.