I think the Fiat would have been preferred for its high altitude performance. The testing was done in february of 43 when they already had the fw190A5 which at low level was the best fighter in the European theater (this was in between the Spit V and IX) The BF109 was already stretching its design limits (its small wings were always its weakpoint), and while with sufficient engines, it could climb high, performance was sluggish. But with the armistice and the impracticality of potential man hours they had nowhere to go they gradually started trying to make up this deficiency with the fw190, first with the D version, and then culminating with the Ta152. They actually instructed the retreating forces to blow up the jigs at Fiat, which they did not do by the way (and the G55 flew, sometimes with Merlin engines with the Syrian and Egyptian air forces).
By the way looking for performance comparative tests I found one that I thought would have existed only in theoretical discussions. The Corsair and Hellcat vs the FW190, conducted by the US Navy.
http://home.comcast.net/~markw4/index1.html
I think the Spitfire production rate is from Beaverbrook times probably, or due to the high variety of different types of Spitfire being produced. I couldn't find an extensive comparison anywhere though. I think the man hours for the Hayabusa could be accurate as during 46-48 months of production only 5900 were produced. The Ki 84 Hayate took only 15000 by comparison it seems
http://www.ww2aircraft.net/forum/aviati ... -3311.html. Shows the difference of a plane that was designed in wartime with shortages and urgency in need and plane like the Hayabusa, where no thought was given to streamlining. I think even though the Japanese never achieved the scale of production of a/c compared to the Germans, their airframe production was OK, you are right that the best way to limit out of scale production historically would be to limit them to their historically woeful engine production expansion. Frankly though the low durability/lack of armor in their early fighters and their slow pilot training process more then halves the later planes combat effectiveness. Plus factor in a lack of supply. Like the Germans, the Japanese surrendered with many intact aircraft that simply had no fuel to take off.
By the way Grigsby's Bombing of the Reich does this by making Italian fighters take two engines (slow production of licence built DBs), and for example in the case of low engine life (Me262) by having 4 jet engines per a/f Edit attached BTR allied fighter table values