An example of how different air forces had different preferences, USAAF tested some Spitfire VA's regarding possible manufacturing in USA. Outcome was negative:
When Ben Kelsey was chief of the Fighter Project Branch at Wright Field before
the US entered the war, he was part of a team that evaluated the Spitfire for
possible production in the United States. The plane was already legendary for
its performance in the Battle of Britain, and the American evaluators
approached the aircraft with mixed awe and enthusiasm. But they quickly soured
on the airplane. As part of the evaluation, Kelsey flew the Spitfire from
Wright Field in Ohio to March Field in California. The trip was a nightmare.
Because of the short range of the airplane, he had to land at a number of
little-used secondary airfields and often touched down with the engine running
on little more than gas fumes. At many fields, engine cooling was inadequate
to permit taxiing from the landing strip to the service area. Long runways on
high desert airfields involved crosswind taxing that burned out the brakes.
The aircraft's marginal stability when airborne quickly exhausted the pilot,
especially in rough air. It was impossible to safely skirt the edges of even a
mild midwestern thunderstorm because of the plane's skittish handling, and what
was routine heartland weather in a P-40--or P-39--was dangerous in a
Spitfire.... In short, there were so many things wrong with the Spitfire from
the American point of view that the Air Corps evaluation board ruled it
Regarding British manufacturing quality, I've understood that one issue of Rolls-Royce factory was that it worked really like a giant craft shop, rather than a manufacturing plant optimized on production economy. Assembling Merlins required lots of hand-fitting and the 'shop floor' would make changes and adjustments to the parts on the fly, not always bothering to inform design people of the changes they had made. This complicated things when US began to license-produce Merlins as their production philosophy was much different.
Packard Merlins had lower rating than RR Merlins, though I don't know if the difference resulted simply from different measuring criteria.
Edit: yarchive.net is pretty awesome, right? Not sure if that account is accurate or not though.
Edited by Brian Kennedy, Yesterday, 12:56 AM.