Gatwick tower advise Gatwick approach what spacing they want.
If there's departing traffic a gap will generally be between 5nm and 6nm for one departure to get away in. Depends on the wind.
If no departures then the minimum separation of 2.5nm can be used when appropriate. Otherwise likely minimum spacing will be 3nm.
The separation on final between two aircraft will never be less than the required minimum wake turbulence separation.
Standard speeds are used.
Continuous descent (low power/low drag) approaches are aimed for by ATC providing track miles when giving descent.
It's the direction you are arriving from that dictates the hold you use, not the aircraft type. The latter would be impossible, or at least vastly and unnecessarily over complicate the airspace for no point that I can see.