If all Imperial Guard regiments would organise local military Olympics (like various military operations (infiltrations, assassinations, holding the fort) in different setup (hive world or ice worlds environment etc)), which regiment will get most medals?

The Officio Assassinorum wins all the medals because the other contestants keep dying of coincidental poisoning. Or accidental drowning. Or tripping face first onto turbo-penetrator bullets. There is a brief investigation into potential foul play, but after one of the referees tragically slips down two flights of stairs and an eversor assassin, it’s rapidly and unanimously agreed upon that everything is above board.