Polax, I honestly can't remember the answer to that from the groundschool days but rest assure I'm not being arrogant in saying I would fly the ECON speed with the relevant cost index. If I did have a dual FMC failure then I would fly whatever speed the aircraft was doing before the FMC packed up then declare unable RNAV and head out of RVSM.
However, if I were to recruit guys then I would be assessing whether the guys have good airmanship and CRM when dealing with a situation on board. Ultimately the guy who has 1000 PIC hours may be more suited to flying single pilot rather than a multi pilot environment. At the end of the day, as I said, put them in the sim and see what happens.