If you have clubhead speed that matches or exceeds that of the pros, then you can get away with playing an 8- or 9-degree driver. But only a tiny fraction of us have that clubhead speed. The rest of us probably need a driver with a loft of at least 11 degrees.
The study appears in the November 2003 issue of Golf Digest.
The crux of the article is that more hangtime with your driver generally means more yards, even though that seems counterintuitive to many golfers. One story told is how the long-drive champions use stopwatches in practice to time how long the ball is in the air. If the long drivers recognize the importance of hangtime, that's a good indicator.
The study examined driver distances at different swing speeds ranging from 65 mph up to 115 mph, and with driver lofts of 9-, 11-, 14- and 16-degrees. For most golfers, it turns out, adding loft to the driver increases driver distance by an average of 10 yards.
At 65 mph, the 16-degree driver was the longest; at 75 mph, the 16-degree again; at 85 mph, the 11-degree was longest (and the 9-degree was the shortest at each level up to this point); at 95 mph, 11-degrees was longest and 14-degrees second-best; at 105 mph, 11-degrees was longest; at 115 mph, 11-degrees was longest.
So if you're one of those golfers carrying a 7.5-degree driver or even a 9-degree driver, do yourself a favor and add loft.
I highly recommended picking up the November Golf Digest and reading this very interesting article.