You'd have to rev it pretty hard for pretty long I think. My crankcase breather is right on the valve on the engine, very close to the cases. I've not spit any oil out yet, and I've blasted down the highway at 90, hit 'redline' at times. Never a drop. I'd say you may have a base gasket problem as another option. I've heard that some monsters leak from the rear cyl base gasket.
Is there no way you can trace the source of the leak. At least clean it up and take it for some short runs keeping an eye on it.
I think the first step is to make sure where the oil leak is from.. Like lrutt said, clean down the area (degrease) and take it for a short spin and check again. If its coming from the breather see if you can see from what area of the breather its coming from, hopefully it's just a simple hose clamp.
I'm not a mechanic, but from what I know the breather is just to release any positive crancase pressure that happens as the gases get past the rings into crankcase. So.. the worst case scenario might be that you have worn rings/barrel and there is excess pressure and its blowing oil out the breather???