The APS would benefit from the government having 4.5 year terms (calling elections after 4).
There should at least be research into the optimal time for a government term, there is no way it is coincidentally optimised at '3 years'.
If it was longer; we wouldn't have to rush projects, be refused to delay deadlines, work on policy that hasn't even passed legislation, we would be in caretaker mode for 6 months every ~54 months instead of 6 months every 36 months - increasing productivity.
The additional capability in having extra time to hold policy trials and see the social or economic results for government (eg nbn, drug test trial, carbon tax, tax bracket changes).
To have data driven policy, we need more time to collect results and amend the policy.
APS leaders tend to align with ministers, so they would retain their positions longer in seeing out government terms - increasing their expertise and giving them the time to have a greater impact on their Departments responsibilities.