That's what we had to do. We went with the blower on the roof. It's almost right over the kitchen window, but we don't really hear that in the kitchen. I do hear it when we walk outside, but it still isn't loud. We do hear the air moving through, but on high, it's quieter or at the worst no louder than my old downdraft was on low. Maybe it's not having the two noise sources together; maybe it's a MUCH better unit -- probably both.

I would have loved to do an in-line muffler/silencer, but there just isn't enough room to retro that between floor joists. Still, I'm happy. On low, the vent is hardly heard in the family room. In fact, we've left it on while we were eating in the kitchen and forgotten it well after we finished eating. That would NEVER have happened with any other vent I've had. So I'd say go for it.

I have a 1000 cfm remote roof blower, but can only compare it to our old remote downdraft, also 1000 cfm, both about the same sound.
My guess would be a 600 cfm internal would be at least as loud if not louder, and 1200 cfm right above my head would be out of the question...

Have you ever had your entertainment interrupted in a movie theatre, by the noise or vibration of the comfort-air system?

While an exhaust system is not necessarily comparable, it is after all, air exchange, involving a motor driven blower and metal ducting.

The point being is, the installation and isolation, especially that of the blower is essential.

I am an advocate of remote blower installation for the higher CFM exhaust systems.

You'll need someone who understands sound and vibration dampening.

Reducing the exhaust systems CFM, below that recommended by the cooking appliances recommendation, is akin to finding an excuse for an incorrect action.