Actually
@S-Man I've just re-read some of the above and realise that the switching noise is there and of the same magnitude with just the drivers fitted driving a 'scaled' load of 100R (12x 8R) via 'scaled' emitter resistors of 2R5 (12x 0R22)... so sort of confirms it is the output transistors and is proportional to the drive and the load. I'm thinking of changing the 220R//C to something like 1k in series with 22n across the bases of the output transistors (for a time constant of 20µs, which is as near a dammit the time of the rising edge) as a snubber whilst keeping the 100Rs in place.