My LHBS recommends, for beers over 1.060, splitting a 5-gal wort between two 6-gal vessels to provide headspace enough to avoid the need for a blowoff tube.
I've got an Old Chub clone going now (this one) that is at 1.078, and because I've had blowoff issues in the past, I did the two-fermenter thing this time: basically 2.5 gal of wort in each, one packet of US-05 in each, to be reunited sometime after primary fermentation.
Aside from the increased infection risk of two vessels, what would the downsides be to this method, versus just installing a blowoff tube on a standard 6.5-gal pail or 6-gal Better Bottle?
Also: I generally don't secondary, but in this case I'm tempted to, if only to get a fermenter back after primary fermentation. OTOH, I will be kegging this one, so I'm considering dumping both fermenters into the keg and "secondarying" there before chilling in the kegerator.