You might be aware of delays now-a-days. If your case went to NSC, I-140 itself is taking almost a year, without RFE. If you get RFE, it may be well over 450 days. Furthermore, I-485 is also taking much longer. You can add at least 6 months just to get interview date and depending on which field office's jurisdiction you fall in, may take few weeks to several months to be interviewed. However, if you file your I-485 now, it is likely that you will get GC much faster because while your I-140 is pending, they will do your background check. You have to decide between gambling $1200 and several months delay. You never know, USCIS is changing rules frequently. I would rather gamble money to save several months.