450 CFM is probably not enough. Look at previous threads on hoods in this forum. They really helped me decide on my Island Hood (also a Best by Broan)

Another thing to consider is the product guide for your cooktop. The Diva website has some technical guidelines, to lead you to minimum cfm requirements, as well as spacing requirements - your hood has to be a minimum height above your cooktop or bad things will happen. In the FAQ of the DIVA site, they recommend 100 CFM per lineal foot, which works out to 300 CFM for 36" of width. I notice they don't make venthoods. Your unit is similar to my cooktop in that they require 30" minimum spacing, most I've seen require 29" or more.

Despite the above, your cooktop is awesome looking & delivers 89,000 Btu/hr. I have to agree w/ chefkev on this one - you need more CFM! By comparison, my Thermador gas cooktop delivers 55,000 Btu/hr, w/ all 5 burners going it gets hot in the kitchen. My venthood is 600 cfm; 400 was available but the product guide & Thermador technical folks suggested that was too low. So I went with the higher flow blower motor. It is variable speed and I can turn it down and do so if appropriate - but you don't want to be stuck there.