I think that for SIDs, the 3.3% figure has been a requirement for quite some time. If conditions don't allow your aircraft to achieve this with OEI, the operator will have to design a special procedure to be followed. This can be referred to as a "Tailored Departure Procedure", "Emergency Turn", "Engine Failure Procedure", or similar.
For the Missed Approach, I agree that there seem to be two different figures. Bear in mind that the MAP will commence at the runway threshold or earlier, whereas the SID commences at the other end, so you will have some "extra margin" built in for the missed approach performance if you're comparing one with the other, particularly on a long runway.
I guess the safest option is to assume that you will need 3.3% for the missed approach, unless a performance specialist can do a more detailed analysis for you.