Your post appeared just as I was firing up the sim to post a shot of my settings. I also turn off motion blur, another “trick” invented to cover low frame rates, likely invented by the same people that think 30fps is more “cinematic”. 
Unless there is another setting I never found, I believe the one you are referring to is “Freelook Momentum”? It’s not really mouse acceleration, positive or negative, more like persistence of movement.
What that does is allow your view to continue moving when you stop giving mouse input, like rolling a free spinning wheel. In fact, one of my old mice had that as a hardware feature. Another feature I struggle to see a purpose for.
I’ve found that lowering the “Freelook Speed” also feels a little better, but only because you have already consciously decided that you now wish to have lower sensitivity, and thus greater mouse input. This means you are forced to move the mouse faster to achieve smaller changes to your view, making the mouse “dead zone” less obvious. Somewhere between 30-40 is okay-ish.
I’d be much happier setting a value to “0” in a config file somewhere, though. I think I’m going to log with with Zendesk, and refer to this thread.