The vast majority of blow-by occurs when under a load and is exaggerated with increasing boost. Simply raising the engine rpms isn't going to present with a lot (pending wear on the engine of course).
Those black circular things at the top of the breather is an oil/vapor separator. Any oil entrained with the blow-by gasses is removed by way of impingement and drained directly back into the valve-cover. As such, it has been my experience that very little oil if any goes out the vent pipe.

And I vent mine into the engine's air filter housing with absolutely no oily mess.

 

Blowby throwing oil around the valves and intentional oil spray throwing oil around the valves are two separate things. I've been told that some 6BT's throw oil around the valves intentionally and make a mess if you run them without covers. Mine does not; seems that I could probably drill an open half inch hole in the top of all my valve covers and not have too much of an oily mess. But other people say their's sling oil like crazy. I don't know if my engine's drier up there than normal or not.


You don't want to feed the crankcase breath back into the engine. Even if all the coalescing filter stuff is doing its job and you have no liquid oil in the vapor, it's still hotter than ambient air and short on oxygen. The environmentally conscientious way is to put it into the intake, the longevity or performance concerning way is to vent it to atmosphere. Of course venting it before your air filter isn't going to be a substantial detriment, but why risk blowing oil drops on your filter or just not giving your engine as cool clean air as possible? And I have seen many a 200,000-300,000 mile engine need a valve cleaning due to oil coming through the crankcase ventilation system; one of the benefits of direct injection is that your intake valves stay squeaky clean, why ruin it?

 

As you well know, the valve-train is lubricated by oil fed up and through the rocker arm pedestals and to the rocker arm shafts and ultimately drips on the valve stems.

That oil drains back to the crankcase by flowing down through the holes in the head/block that contain the valve push-rods. That passage is rather narrow.

When on the throttle hard, producing more blow-by gasses, those gases pass up through those same push-rod tubes. If there's enough blow-by gasses rushing through those tubes (WOT ?), it will entrain some of the draining oil.
Those Case valve-cover separators work very well at separating the entrained oil from the blow-by gases.

Pending the wear on the engine, the amount of boost (blow-by), etc, a little or a lot of oil is picked up.

Certainly those gasses most likely do not support combustion of the fuel, but unless your engine is stupid worn out, it shouldn't (and doesn't IMO) present a problem.

I think with well over 400hp to the ground, taking this 6400# heap for a high 12 second 1/4th mile pass, the blow-by has apparent negligible impact in my case.

 

If you vented it to atmosphere you'd probably be making 650 HP and running high 9's.