I have both. The P-51 is an absolute blast to fly - I enjoy it more than the Corsair. Maybe because it's new, but it seems much more solid.
Here is my review:
Since I wrote this, I was able to move the battery back a little and eliminate the nose-up trim. So now rolls are much better and pretty axial.
I am not great at knife edge, but the P-51 seems easier - less coupling between the rudder and roll.