Thanks for the tips Noel and Mac

It appears the advantage of the fast rendering is the convenience and speed (an 11m song took just over 2 minutes!) And sound quality (to my ears anyway) seemed identical to real time recording.
However by recording in real time into Adobe Audition, I can edit each real track individually as it is being recorded (volume, panning, reverb etc) I can also see the waveform for spikes etc

after a bit of thought, I will probably stick with Audition...

thanks again
Mal