books can only give you an average time frame.
I'm guessing you're fermenting at slightly above 'ideal' temps and thus your fermentations finish faster.
More importantly though, you need to wait for the beer to finish primary before you rack it. moving 'as soon as the krausen falls' is not a "surefire" method for success, especially as you start brewing bigger beers.
plus, some yeast strains krausen doesn't fall when primary is finished...instead it stays, protecting the beer.
you rack to secondary after 7-10 days (that's the minimum)...and once the hydrometer isn't falling anymore for 3 days' readings.
I will say 1.040 to 1.006 is pretty low...either you had a pretty attunuative yeast, or there could be a little something else in there eating the sugars up (wild yeast, etc).
Either way, I wouldn't worry about it. Just slow down on the racking, as pre-mature racking stresses the yeast, and stressed yeast produce off flavors.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10