6k would be a no-brainer.
In our office, we'd definitely need the enterprise version for compliance reasons, not because of the features. That's about 14/user/month.
At a workforce of roughly 2500, that's a 4million+ yearly cost for something that is comparable to something you can get without that pricetag. It's no competition at all at that point. Think about it, would you be willing to ask your boss to pay 4 million so you can have a different chat app? No matter how much more ergonomic and friendly and intuitive it is.
I feel like most Americans don't appreciate the financial constraints under which European startups are operating :) The median series A is something like 1–6 million Euros over here. You have to seriously consider what you spend money for on these scales.
That would be 420k/yr. To get to 4 million you need 25000 users. That's quite a big company.
That's a very upside down way to think about it.
The question is: "are staffers $14 / mo more productive with it, than the free version?"
The answer may also boil down to satisfaction, support calls, other things, aka 'total cost of ownership' as well.
Not 'But it costs $X million!'.
Companies will spend a fortune giving staff the right monitor, or chair, but literally don't think they're smart enough to know the dam tool they use all day?
Let them pick their chat software, like they pick their monitors.