Here is my suggestion.
If you have received FP notice and RFE, do FP first and respond RFE about a week or two later. FP doesn't generally trigger any manual action because it is all automated. But RFE response means, INS has to locate your file and place the documents in same file.
When they open your file to place your response, they check to see if any action needs to be taken, say your case is > 20months etc. If your case qualifies to be sent to officer, you don't want them to notice that they are awaiting FP results and can't process your case!. Worse, they may PUT YOUR FILE aside for long time, until next RFE or some thing !
This has worked for me and other in 4 - 5 cases of my friends. And unfortunately couple of my friends reponded for RFE first and FP later, are still awiaiting approvals.
Anyways, good luck