That's what I was initially thinking as well since the Tempest's prop is actually larger than that of the F4U's prop (14' 0" vs. 13' 4" for the F4U-1's +, 13' 2" for the F4U-4).
But perhaps there's some kind of equation there somewhere. I mean the P-51's prop blade is far from a toothpick, even compared to the Tempest's prop. Judging by the relative tiny size of the actual Mustang when compared to the gigantic Tempest, the prop might be more efficient for the P-51 than the Tempest's prop is for the huge Tempest.
Looking at the official tests, it seems as though the P-51 somehow creates more thrust or something as it turns better than the Tempest despite the Mustang's slightly heavier wingloading (P-51B weight @ 25% fuel, full ammo, clean/wing area: 8,604 lbs./235 sq.ft. = 36.6 lbs./sq.ft. VS. Tempest V weight @ 25% fuel, full ammo, clean/wing area: 10,525 lbs./ 302 sq.ft. = 34.9 lbs./sq.ft.).
Even through that, the Mustang turns better so the trust factor (which seems very evident in our current F4U) must be helping turn rate or turn radius somehow, though I cannot fully base my opinion on the F4U since I truly do not yet understand the equations which determine the Corsair's amazing turn rate.
