Civil Service salaries are conspicuously unequal, per pay grade, between departments; some are "more equal than others". I recall one former tax office worker who was staggered how much more he was getting, for the same grade, in the same town (ie it was nothing to do with regional variations, such as the high-unemployment northeast getting thousands per year less than we got, in the southeast).
Performance bonuses are based on annual performance review "box markings" but, as it is not possible to be privy to how productive your colleagues are, I always took the cynical view that it was more a measure of social skills.
As for bonuses for the higher-ups, these are really a reflection of how hard their workforce are working and it is a real kick in the guts to see boss awarded thousands for your hard graft while you get a measly hundred or teo. For the year! Really motivational...