I'm not sure about an upper limit cap, but I've come to the realization that Off/Def IQ might be underrated by many. I'm starting to think that the value of an A+ is pretty high.
I can see the argument that it's a decimal behind the scenes, sort of like FT%, that is used as an efficiency multiplier. I would doubt that there's something like a 105% or 110% in Motion, for example, but to my above point, I think the difference between 88% and 98% can be pretty big (B+ to A+, in theory at least)