i guess your estimate is right and wish it could be sooner.
1) the biggest problem is fbi name check. things keep changing from time to time, if yours has been done before the transfer or is sent to fbi right after it, that's good. from what i read, the check process could take 3+ months;
2) then it all depends on how many officers are actually processing gc cases at baltimore. i believe it's next to none at this moment (because i went there 3 times between this mar. to july, nobody was waiting to be interviewed). last year at peak time, it was said 14 officers were working on gc cases everyday, and another 15 (+-) on citizenship cases. but this is hard to predict. local offices are quite different from each other, and from time to time, and even from officer to officer.
3) new policies or procedures may come any time. this may change the processing time dramastically. this is espescially true for the fbi name check, which was introduced last nov.
4) you never know if your files are in order. like in my case, medical forms were not complete (not my fault). and do you know how much damage it caused? almost a YEAR already!!! my friends had interviews the same week as i did, they all got approved right away and mine was delayed. then this new rule came, then baltimore officers worked on other stuff (special registrations i guess), then nightmare came ...
good luck!