If one assumes that the requirement is to be 'stable' by 1000ft agl (ie landing flap and Vref+15 max with gear down), then with modern jet transport performance, then 210kts at 12nm on the g/s works well - call that Gate 1.
In level flight a modern jet (zero wind, anti ice off) decelerates at 1 kt per second.
So one could be at 320kts 110 seconds before 12nm finals as above, average g/spd = (320-210)/2 = 265 kts * 110 secs = 8.1 nm.
So, about 20nm to run at 320 kts level at 3800ft aal is about the max without using early gear or speedbrake.
By inference, 320 kts at 6000 ft aal is going to need remedial action!
As has been said elsewhere, it is nice to know the limits but it is preferable to land rather than go around, all for the sake of 5 seconds earlier on stand.