RIR convert to Perm?

I'm EB2. My RIR (Mar. 2005) is in Backlog center without getting a 45 letter yet.

Is it possible to convert my RIR to Perm. By looking at the visa bulletin, it's quite possible the priority date for EB2 will become current soon. But waiting for my RIR will take forever. Can anybody please tell me is it doable? What's the disadvantage and advantage by going so? How long will it take?

Many thanks.