The maximum SPL of almost every condenser microphone is determined by the overload point of its electronics. Practically speaking, capsules are never damaged by sound pressure alone. The diaphragm in a condenser microphone is held under tension, and hardly moves even when incoming sounds are very loud.
The KM 88's capsules were a special case because their membranes were made of ultra-thin nickel foil, which is both physically fragile and electrically conductive. If someone (or something, such as strong wind) actively blows one of the DC-polarized membranes into contact with the backplate, electrical arcing is liable to occur, which can perforate that diaphragm at the points of contact. Partly for this reason, the polarization voltage for this type of capsule was held to 40 V rather than the more usual 60.
The KMF 4 on the other hand used a Mylar membrane with its non-sputtered side facing the backplate, so it's not vulnerable to arcing and perforation should it be forced against the backplate. Instead, it's just vulnerable to the "usual suspects" for all condenser microphones: dust, liquid spills, condensation from the breath of people who sing or speak directly into the microphone without a screen, and especially the gunk in such people's breath if they smoke (or if they record right after eating without brushing their teeth first).
You also have to watch the Lemo connectors in these mikes--they can become intermittent, and then they need to be resoldered.
--best regards