No. Sentience (or more accurately, sapience) has no preset range to qualify other than it is capable of understanding the same sort of concepts in life commonly expected of such a level of development. IQ and level of intelligence after that point can and will be totally variable after that, with some higher and some lower.

Besides, humans all have widely varying IQs, yet all of us still qualify, so why expect it to be any different with other species?

No.

More or less, as they are written by humans. We are constantly told the augments and the Vulcans are many times as intelligent as humans. But it never shows.

Personally no, and I think every species has a certain type of intelligence that they excel at better than other species. Vulcans are highly logical and have strong number smarts, but they aren’t as good at the emotional aspects of things. The opposite can be said about Betazoids, they are highly emotional and in tune with emotions and feelings, but this can come at a cost.

And just like humans, different individuals can have many different intelligence types and personalities, even if they are from the same species. Simply look at Spock and Sybok. They’re both Vulcans but have very different personalities and intelligence types.

I don’t think that anyone would claim that the Pakleds and the Q have comparable IQs.