AD means different thing to different ministries due to work requirement - for ministries such as MFA and MTI, they have to frequently face their overseas counterparts so must have higher-sounding titles, not so much to fast track them. tehre are ADs from those ministries who move to other ministries and had to make do with much lower titles.

for grades, the salary is like this:

mx 12: 2550 - 5130 (AM, Mgr)
mx 11: 4100 - 7190 (Mgr or AD)
mx 10: 6350 - 10400 (AD, DD)
mx 9 (superscale): 10580 - 16540 (DD, Dir)

the above excludes the usual bonus and variable components, which would usually add up to a total pay of around 15 to 16 months of the monthly salary...