This is all I found on Alla and BG.
"I was able to 4-hit with a non-usu 5-hit build (including carbonara) and SAM roll. 31 store TP from gear and carbonara, +42 or higher from a 6 or 11 on SAM roll. I don't know if there's supposed to be a total store TP cap, a gear store TP cap, or something else, but it is entirely possible to 4-hit with SAM roll. I would imagine that, given current gear progression, a 4-hit would eventually be feasible with carbonara and store TP atma(s)."
This was off wiki.
"Store TP caps at +51, not +50... I did tests with my gear merits and food I had a total Store TP of 77
my tp should've gone 20.3, 40.6, 60.9, 81.2, 101.5 (total 77(+52))
but it went 20.2, 40.4, 60.6, 80.8, 101 (Total 76 (+51))
it if was (Total 75(+50)).. it would be 20.1, 40.2, 60.3, 80.4, 100.5 etc etc
mob did NOT hit me, seigan third eye, and Zanshin did NOT proc 5/5 store tp merits, and no they dont increase cap. why +51?! go look at hasteĀ :) you really need +26 haste to get the +25 cap "
"On your analogy to the haste cap, the 26 haste is a cap for 25% actual haste because of how the game handles fractions (or at least how we think it does). Since the 1.XX modifier where XX is your Store TP seems to work for calculations, it would be more natural to surmise that the game caps your multiplier at some percentage. 50% or 75% boost would be two likely levels, but we know you can go beyond 50% so throw that out. It might be that 76 Store TP nets you a 75% boost, similar to haste, and that the cap is 175% of your normal TP/hit. If this is the case then 76 could be the actual cap due to all contributors (merits, job traits, gear, food) and not represent a 51 Store TP gear cap. COR seems to be above and beyond these calculations allowing you to essentially break the cap."
So basically, no one knows WTF they are talking about. I'm sure SE must have imposed some sort of Store TP cap, because as more Store TP gear comes available, some jobs will be broke as ***. COR roll obviously breaks some sort of boundary. Some players notice a cap, some don't. I think it's save to say, no one has actually tested Store TP potential fully except for reaching x-hit build.
Edit: IPhone double paste derp.