The P-40 is one of those planes for which you'll find a different number from practically every source. From various sources, I've seen figures ranging from as low as 317 MPH to as high as 365 MPH for the Kittyhawk. Since the Kittyhawk had a reputation for being able to outrun the Bf-109E at low to medium altitudes, I'd expect it to have a top speed of at least 350 MPH which matches well with the AH version. I do not believe the higher (360+) figures; later P-40's with less weight and more power could barely make 370.
The P-40C was certainly the slowest of the entire P-40 line. It had the weak early engine, the draggy body, and even more drag from the bombrack. 335-340 MPH is likely about as fast as the P-40C could go; the P-40B would be a hair faster but not much.
From the side the Tomahawk and Kittyhawk look very similar. However, look at them from the front sometime, in person if possible. The P-40B/C is a lot "rounder" than the rather narrow P-40E.
J_A_B