I have a Bosch. It raises up 10" and has a 600 CFM blower. It was the only one I could find that raised up that high. It comes in stainless, bate ordered a black top to replace the stainless one so it would blend in with the cooktop. My cooktop is in a diamond pattern and the downdraft does a great job on the back element, a good job on the middle elements and adequate on the front element. 600 CFM is okay, but 1000 would be better.

lindainct, we have a Thermador cook'n'vent with the telescope. No longer made but I would imagine it is very similiar to the stand alone Therm. telescope. I also had an old JA. Believe me the Therm telescope does a far better job. Ours is short run, about 8ft and the inline works fine. (I think it is 5-600CFMs) Low is all I ever need to run it on. If I have lots of steam going on the front burners I tilt a pot lid to aim the steam.

Thanks for your replies and suggestions. I have to make a decision this week and will post my final selections.
Linda

I just installed the Thermador UCV236DS coupled with the 600CFM integral blower. This is 14 inches high and works so-so on low, very well on Medium and extremely well on high. Our ducting is rigid ducting vertically down, then one 90 degree turn, and then 15 feet of straight ducting before breaking through the wall to the outside of the house.

I don't know what adding 15 more feet of ducting would do to your CFM requirement but I just wanted to give feedback about one model.