if we had reset the FCMC one at a time would it have helped?
Absolutely yes.
and you reset the FCMC in flight?
It is allowed from the QRH, so why not ?
how much would the extra fuel burn be flying an acft not at the optimum CG?
You should find the value in yor company MEL. Search for the xftr sys inop and you'll see limitation(s), if any, and fuel consumption penalization.
Ciao