Funny how this discussion took a turn. Getting passed over was my grand plan from the day I got my wings. I didn't intentionally do SOS (though offered twice in residence), got passed over twice, cut my ADSC by 2 years, got my severance pay, got a reserve job, landed an airline job, and the rest is history. It took a lot of planning and gut wrenching decisions but it paid off in the end. I did SOS by correspondence just before I separated, so that I can be promotable in the reserves. Back in the day, if you wrote the promotion board a letter stating that you did not want to get promoted, they definitely would not promote you but you would also not get the severance pay.
Back when I was in, you can continue to 20 and retire as an O-3 as long as you were in a "critical" career field. And yes, O-4 can continue to 20 and retire with no issues.