As far as I can recall the Avon as fitted to the Comet were expresed in RPM I seem to remember 12k being about max - Now we come to the Spey as fitted to the 1-11 100% HP rpm (high pressure turbine speed) this should have been full power - but oh no they started blasting demin water into the thing then (as far as I can remember ) full power then became 107.9% - you must remember there was no A/T in those days
The Comet also had a thing called a thrust lost indicator for each eng which under most curcumstances was the governing factor a to whether or not to continue the T/O if the needle was not at 12oclock when the throttles were opened.
All this made the British A/C industry what it is today!!