My comments did not assume a sub, and it didn't sound like Odnok was considering one as well.
Yes, I agree with you there are compromises. One more you didn't mention is that the speaker with the higher cutoff will also probably be more efficient and require less power.
I am using a 4 way speaker (sub built in), where the sub goes to 18Hz. Granted, not a lot going on that low, but it's great to know that if it is present, it will get attended to.