According to E. Michael Johnson in a May 2011 Golf Digest article...
The results of a 2009 launch-monitor test by Golf Digest found everyday golfers who swing less than 85 miles per hour actually carried the ball five yards longer with a 4-wood as opposed to a 3-wood, while those swinging more than 85 mph hit the 4-wood eight yards longer. (Elite players still hit 3-woods farther than 4-woods). In both instances the ball went higher too, providing a softer landing for those using the club on approaches into greens.
Read More http://www.golfdigest.com/golf-tours-news/2011-05/golf-johnson-equipment-0530#ixzz2EbC9HBwc
Above article link also has info on Tour pros and the 4W.
This summer, I went from a Calla X.Tour 3W (15*) and a 19* TM Raylor (5W, more or less) to a RBZ 3W.HL (17*, so it's a 4W) and an RBZ 7W. Had hook problems at first (regular RBZ FWs have slight draw bias and a 45 gr. shaft), but a thicker grip seems to have lessened this problem.
Anyway, when I swing smoothly, an OK hit with the "4W" goes 210 yds., about 10 yds. longer than an excellent hit with the old 3W.
- Really test hit any FWs - especially those with lightweight shafts - to make sure they fit your swing.
- Look at the specs sheet for the model before building a new FW mix. The RBZ "4w" and the 5W are only 2 degrees different in loft. I dumped the 5W - fortunately before I hit it - in favor of the 7W.
Basically, 4W = 17*, 7W = 21*; 4W had an inch longer shaft.
So... 4W goes 15 - 18 yds. longer than the 7W.