Keg,
The big efficiencies are achieved in the aircraft that Mainline operate.
It was reported last week that as the 767 retires & are replaced by A330's domestically.
Rationalising the domestic operation to two fleets types, the operating cost would reduce by around 10% and would be within (If my memory serves me correctly) about 5% of Virgins.
These efficiency gains were achieved without ANY changes to the Long or Short Haul EBA.
Considering crew costs are only about 3% of the airlines operating costs, it pales into insignificance compared to operating fuel efficient jets.