Could the oil conversion alone make 26-knot Queen Elizabeths?

Could Admiralty planners reasonably expect the late change from coal to oil to make the historical Queen Elizabeth design exceed 25 knots?

No. The Director of Naval Construction's performance estimate was accurate to about a quarter knot despite the redesign.

Oil firing improves combustion and endurance at high power, but it does not erase the machinery and hull choices already fixed in a coal-fired design. The Admiralty had detailed calculations for the altered displacement, boiler plant, and expected speed. The resulting estimate missed practical performance by only about a quarter knot. A genuine 25- to 28-knot design therefore required small-tube boilers and integrated planning rather than optimism about the fuel change alone.