The trends I have been seeing over the last year, monitoring several different forums and data aggregators, are as follows (percentages are rough but fairly accurate):
20% - 30% - Get approved for a EAD/AP Combo Card pretty quickly (Within a couple of weeks after the biometrics appointment)
50% - 60% - Get the EAD fairly quickly but the AP drags out several months
The remainder seem to have their EAD/AP applications get stuck in limbo and don't get either of them adjudicated prior to the Green Card being approved
CAVEAT - It seems that USCIS is pulling a lot of AOS applications from the top of the pile in the last few months and many applicants are receiving interview notices within a month or two of their biometrics and this is causing many more people to fall into that "Remainder" category lately, where they are getting their green card interviews before EAD/AP is processed and/or they are getting the approval(s) between the time they get the interview notice and when they go to the interview.
2ND CAVEAT - This is all anecdotal "evidence" as I said above, I spend a lot of time on a lot of different forums and data aggregator sites (this whole process has grabbed my interest LOL) and none of this is "Hard Data" so take it FWIW Good luck on your journey!