I am confused that some people here stated it would be better not go for premium filing for 140. If 140 is not processed, then your 485 will not be processed. (Is this a true statement?)Thus, by paying $1000+, you will cut back a couple of months of waiting time to have your 485 processing started.
Of course, if your case is weak, you may get RFE. Then it is a different story. Say, you are EB2, working for a big company, you should be fine.
Please correct me if I miss anything here.