The amount of oil the provent collects will only be an average, it will vary between engines, mileage of engine, etc etc..
The biggest issue with a modern common rail diesel engine is not particularly CCV (Crank Case Ventilation) recirculation or EGR (Exhaust Gas Recirculation) its the combining of the two. The oily fumes of CCV and the dry exhaust soot mixing together that form a black sticky tar like product that collect in the intake, its the biggest cause of EGR, intake related faults, valve issues etc etc.
By isolating one or the other, using either method such as a provent or EGR blanking on upto early Euro 4 spec engines, or on later Euro 4 spec engines and Euro 5 doing EGR emulating or remapping to delete the EGR function is one of the biggest positive things that can be done.
Personally I tend to go with EGR blanking, deleting through remapping or emulating to be a better solution as it also removes the by product of exhaust gas being “re-used” in the combustion process, thus leading to cleaning more efficient combustion, which in theory should give more power, but more positive will give better fuel comsumption and a longer lasting engine, of course when combined with regular (10,000km) oil changes and air/fuel filter changes, again at that 10,000km service interval.
Just food for thought, nothing more.
A provent is one positive “mod” to do for very little cost.