Look left, I have not operated under the exemption for some 15 years and mainline virgin have never used the exemption.
That all said you are correct, they use the limits as targets but why wouldn't they? It is the same as max takeoff weight, Max landing weight, Max zero fuel weight etc ...if you don't target the limits then you are leaving payload, productivity or whatever you want to look at behind.
Virgin has been using a FRMS quite successfully since 2007 ish and it works as well as can be expected.
We as pilots are still miles in front of junior doctors who works crushing shifts and they too have the power of life over death - doesn't make it right just making the observation