You will get more info on this from the appliance experts over on GW's Appliance Forum, link on Kitchen page. There are several good threads just now on range hoods. That said, most everyone there has gone away from gas to the sleeker, cleaner induction, and no longer need a lot of hp in their range hoods. Good luck!

I would disagree with the "induction cooktops need less ventilation" assessment. I have a Miele KM5753 induction cooktop, and when I'm pan-roasting vegetables or pork chops, there's as much steam and smoke coming up as from my old gas range.

Heat is heat, regardless of the source. Induction may not add the carbon dioxide from burning gas, but it still heats up the pan and makes a ton of smoke and grease.

I have a 900 CFM hood, and sometimes I have to turn it up to the highest speed, before I throw the veggies / chops into the heated pan. I really doubt 300-400 CFM would handle the burst of steam. Grilling, by the way, is even worse for ventilation.