The other option would be a fan controller - though I'm not sure if a throtlled back Delta screamer would still be noisier than a fan designed for lower CFM to begin with.
Some chipsets have speed control that can be activated by Almico Speedfan, but that's no help with a Delta, as that beast should not be motherboard powered.
If the heatsink can take it, it might be worth looking at TMD fans - but they seem to only be available in 70mm size.
TMD (Tip Magnetic drive) relocates the motor to the corners, so the fan has a very small hub area with less dead zone.
Another option is an Aerocool blower, that has NO dead zone
http://www.amdmb.com/article-display.php?ArticleID=239&PageID=4
- But following through this review, it did NOT perform well on an AX-7.
PAPST (PABST ?) seem to be the name to look for in low noise.
And finally
http://www.amdmb.com/article-display.php?ArticleID=155&PageID=2
AX-7 reviewed, with varying fans - easy to see why the blower (or the TMD) would NOT be a good choice - the entire profile is set for the main airflow of an 80mm fan.