There is no doubt that the Merlin powered fighters were the top pick, though I have some thoughts as to how production limitations, both in the late 30's and early war period to the end of 1942, were viewed by Lord Beaverbrook's minions when planning an air arm that depended on this liquid cooled device not only for fighters but four-engined bombers as well. What would be the definitive source of Merlin production data?
I'd like to expand on my post 9 of this thread. I'd stated that I would have liked to have seen some of Blackburn Aviations radial engined single engined aircraft maintained in production, even if only on a limited basis. That Blackburn and its major subcontractor, Boulton-Paul, were not afforded consideration for design production may be due to the failure of the BEF missions early on. It isn't the successes that stuck in the minds of the British leadership, like some of the Norway events, it was the failures such as the Aachen raid. I mention that the Royal Navy pulled aviation sections from cruisers and capital vessels, supposing that all support could be provided by land-based aviation. This occured in December of 1941, all of the aviation sections removed from the ships in a day. I consider this one of the errors of World War II.
In early 1942 the Japanese wished to consolidate their holdings in Malaysia. A task force was assembled to carry out Operation C, the consolidation of the Western flank of Japanese expansion. Admiral Nogumo's job was to attack allied shipping and challenge naval force in those waters adjoining Malaysia to the Indian Ocean. No further invasion was ordered,no more land to be taken. The fact that RN ships, sent to the area hastily apon the Malaysian invasion, were stripped of their aviation capability led to the sinking of several by Vals and the unchallenged sinking of 30 merchant vessels. I can cite several other events where the products of Blackburn or one of the other smaller production facilities would have been a welcome sight in the sky to a sailor.
You mention the 'stretch' of the Spitfire. I've noticed this in several other aircraft of the period, called on to soldier-on with an increased payload. This seems to have put the spur to increased engine power output, the number of hours one could expect from a powerplant's useful life decreasing rapidly. I believe the Blackburn effort could have been 'stretched' for the mission at hand, though with the constraits of a radial engine. Regards