PUDOC, not jumping any throat here, but the OP wrote about flying on an OCEANIC TRACK and he supposedly flew it in FMC ECON, then perhaps, FMC LRC.
OCEANIC TRACKS are flown with ATC assigned fixed Mach numbers, period (maybe the OP is a Flight Simmer, that I don't know).
Yes, you can request another Mach number, but ATC never assigns "ECON" or "LRC".
The FL the OP mentions, F330 and F350, is in the band where MNPS rules apply.
Yes, if you are an operational maritime patrol aircraft, you will fly far below RVSM and MNPS, and then you can do as you please for operational reasons. However, the designation -400 as mentioned, and the OFP and economic considerations make it clear it must be a commercial aircraft operation the OP is writing about.
Ian W - geographically speaking, flying from Portugal to the Canary Islands is a stretch over Atlantic Ocean water, but is not an Oceanic track in the meaning of ATC, that stretch is just another airway. On an oceanic track, you are not free speed, unless it is busy - as every operational long hauler will know, your oceanic clearance will contain route, flight level and assigned Mach, often also an assigned time for crossing the oceanic entry point.