It may be worth noting that Boeing is evaluating the rejected takeoff flow and may as a consequence may eliminate the manual deployment of the speedbrake as oposed to the auto deplyoment with reverse thrust. In the past a carrier could go to Boeing and ask for an NTO regarding this facet of the rejected takeoff. For the last six+ years Boeing would not issue an NTO for this alternative procedure due to some previous accident investigation. Not sure how Qantas gets around this with the B737 but perhaps this is jut a FAA mandate and the Australian authorities look at it a different way. I must confess, I have fumbled with this procedure in the simulator on many occasions.
Also, IMHO, a Master Cautiion light is no reason to reject a takeoff when you are above 80Kts, unless you have specifically briefed it as such.