Your thinking was spot on, that fan should be more than enough , and having a sealed vented hood is a major upgrade from the el cheapo wing ! Dont second guess that choice.. Sealed Vented Hoods for the win , you bought the right thing, you just need to make sure its configured properly, and after that , If the fan is still not cutting it , I would suspect a fan problem. What is the fan specs, brand and cost? Did you get it from somewhere that will exchange it for a different one if its faulty?