Welcome around and congrats to your first post here
Caps and caps, there ain't no hard caps but just what the variables in the PUP-formula gives. Some players managed to get hold of uber stuff during a short window (don't remember if it was a bug or a test) and they can pass any limit imposed on normal guys.
See the stickied RE 101 and find the formula for PUPs. That will kind of tell you what is a theoretical "cap" but it is that real-luck factor that can cause some PUPs to be better. But that is rare and should only happen if the result from the formula is quite close to next integer.
/Zimoon