What I have noticed with summarized data in Quickbase is it will never warn you when it isn't able to summarize it all. It will present inaccurate data to you instead and you won't know unless you are auditing it.
We had issues summarizing numbers and it wasn't the length of the numbers it was the amount of data combed over I think. It was for commissions for an entire month and what we noticed is when we filter for specific locations we get accurate data but when doing the calculations for all locations at once it skips data in random places and the numbers do not add up.
I anticipate this to also be an issue with formula queries but I have not seen it in action yet because I have not had to grab and summarize that amount of data with them. It is also entirely possible because formula queries leap frogs the typical relationship it may not be subject to this same issue. It may depend how many levels of related data there are as well. Just figured I'd throw this out there though in case others have noticed issues like this.