Both aircraft are fairly close in top speed, though the 1A has a very slight advantage (couple mph at most). The 1A also has a small advantage in turn radius (few feet, so practically negligible).
However...
- 1 I believe has somewhat larger fuel tanks.
- 1A has much improved visibility due to the bubble canopy.
- As noted, the 1A generates slightly more HP out of its engine, comparible to the F4U-1D.
- The 1A we have I believe is a later block that also has the larger paddle-bladed prop used in the 1D.
- Because of the previous two points, the 1A has a SIGNIFICANTLY improved rate of climb and acceleration, and is superior to the Birdcage in any vertical maneuvers. This is the biggest performance difference between the two.