Perhaps, check out the Can-Fan Max Fan Pro product line. I have a Can-Fan Max Fan Pro, 6 in, 420 CFM. It's well designed and constructed, is Can-Fan's (biggest fan co.?) top-of-the-line, has 3 speeds (I run on medium), is a relatively new model, is quiet (particularly with a muffler/exhaust and filter hooked up), and is available at good discount cheaper than competing fans which make a lot of noise about being quite, but the fans often aren't all that quiet if you check the specs and reviews.