really has little to do with the initial gravity...a lot more to do certain grains being present, available headspace...and really the yeast strain.
wit yeast strains are known to blow off really bad, yet take a little longer to ferment fully.
Its one of the key reasons I stick to a 7 gallon bucket fermenter...usually there's enough headspace that I need no blowoff tube. unless I pitch onto an existing yeast cake...then it gets messy
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