Promotion up to Flt Lt is on time rather than on merit and so it will make no difference whether you are FJ, ME or RW.
There is scope within the system for 'exceptional' individuals to promoted early, but I can't think of a single aircrew mate that has benefitted from this - only adminners, whose bosses know how to fill out the appropriate paperwork. In fact, it appears that only useless adminners don't get accelerated promotion to flt lt (so AG had best get used to being a fg off!).