I actually registered just to tell you about this one! I know your heat woes, and I have tried 900 ways of cooling it down. As far as a 700 or 800 cfm fan, I don't think its possible, short of a jet firing off in your garden. Keep in mind a 300 cfm inline fan, costs several hundred dollars. So I'm gonna let you in on a very good secret, started by some potheads somewhere. I'm not gonne get into the details, because its alot, but its hands down the most effective economical inline idea ever. I assume you are using an air cooled hood by the way, if you are looking for a regular fan, thats never gonna cool a 1000 watt HPS. Google "Stanley Blower Mod", and read all about it, use one myself on my 400watt HPS

Wow, thanks stefang you just saved me 200 or 300 bucks! I can't thank you enough. It also looks pretty easy to set up to. May your garden grow well.