Update: since swapping the PCV valve myself (the old one was definitely shot) and getting the car back I've put on a few hundred miles, mix of casual and spirited driving, I haven't lost a drop of oil, nor noticed any spatter in the engine bay.
It may be placebo but I could swear that the engine is idling more smoothly now.
The only thing I can think caused previous spatter was oil mist from testing the oil filler pressure settling and causing a visible contrast after the fact. Did not notice any visible spatter when checking, only after driving afterwards.
Fingers crossed this is the end of my consumption issues but will be keeping a close eye on things.