I concur wholeheartedly with WizofOz - when you're looking to get down and slowdown, in the 73 it seems to work much better if you get down first, then slow down. The SB is definately more effective at high speed. I also can't see the point of intermediate SB positions.
It's best to sort it out early if you're high. However, sometimes you are held high by ATC closeish to the field where some thought is needed. Asking for extra track miles is probably the most sensible. However, cranking the speed right up to 320kts with full SB will give you very high rates of descent (especially if you are ACCELERATING to 320 i.e. slow down if you are held high - just like VNAV PATH does). However, if you think it's gonna be tight (we've all been there) consider limiting the speed to 270 so you can take the gear early - haven't investigated scientifically but, IMHO, I reckon SB + Gear at 270kts is a steeper descent gradient than SB only at 320 kts. Obviously this kind of thing should not be routine but a 'get of jail card'.
Having a couple of mental 'gates' in mind helps. Eg at 20miles you would normally expect to be at 250kts and 6000ft AAL. If you're at 4000ft AAL, you can afford to keep high speed and you won't need speedbrake to slowdown is one I find helpful. After all, SB is a grubby tool isn't it?