It's probably a more complicated question to answer than it should be, so this post is probably gonna be really boring, but here goes.
It all depends on how you choose to hear it, in a way. Academically Private Ale is nowhere near their fastest song, as that link Jon shared states, because while the music is at 196bpm the vocals are in half-time, so it can feel like 98bpm. The fastest song on Kerplunk by these standards is Strangeland at 214bpm. It's difficult to judge though because a lot of their songs actually have a double-time feel, based on the amount Tre uses the snare, and the more snare there is going on the more momentum a song has. There's an important distinction between tempo and momentum; if you took any given song and took the snare out, but left everything else exactly the same, it would feel slower. Plus Billie tends to throw in a lot of insanely fast strumming fills, where he'll hit the next chord slightly ahead of the beat and strum it a couple of times in double-time (so if the song is already in double-time then it's effectively quadruple-time for that split second).
So to take Strangeland as an example, 214bpm is ridiculously fast and if you were playing to a metronome you'd have it set to half that, but if you were to write the sheet music out at 107bpm rather than 214bpm it would be super messy and difficult to read. I hate applying academia to punk, but I think it's interesting in this case. To throw a spanner in the works, Jaded is 160bpm but with a double-time feel, making it effectively 320bpm.
I haven't gone through the rest of the albums but I can go into more boring minutiae about any specific song if anyone cares.