I have used that yeast but not in something that high (mine is a Belgian Pale Ale). It attenuated very nicely, about 6+ ABV.
Most of the O2 is required when the yeast are building their cell walls and getting ready for the exponential phase, So I would say by the time you are seeing krausen there is no longer a benefit from additional oxygen.
Something is always fermenting....
"It's Bahl Hornin'"
Kegged: Bourbon Barrel Imperial Stout
On Deck: German Lager