[{HVY-E}Jinxx]

Well, I guess I'll throw my .02 in.

Everyone here knows my preference of plane.... DUH!
The P51 was MUCH better then the Jug down below 12000ft. Once you get above that, the P51 falls off dramatically in power due to it's gearing of the supercharger and lack of a turbo.
It was quite common for the P51's and P47's to fly next to each other and then at about 15000ft, the P51's would look over at the Jug drivers only to see them looking at them and pointing up. The P47's would then push the throttles up to Ludicrous Speed and out climb them all the rest of the way up. Since the P51 doesn't kick in the 3rd stage of it's supercharger until 19000ft or so, the P47's would be long gone and already at 30000+ ft. I have quite a few stories from pilots on both sides about this feet.

As far as the P51B goes, well, from everything I've read about it and from talking to WWII Pilots from the 332nd when they came to Ft. Bragg, it was a bit under powered. The P51C (Mustang III) was the fastest P51 at alt. Capable of keeping up with a P47 until about 25000ft, and the guns commonly jammed on all versions of the P51 due to the off canted mounted they needed. This was due to the Laminar flow wing. It was improved with the D model, but still jammed with excessive G loads.

Now, as far as best fighter at the end of the war...
There are quite a few reports of US pilots, P51 drivers, flying around in Ki-84's stating that it was the by far the best fighter out there. It just came a day late and a dollar short. Just like the German's ill fated ME-262. Many US test pilots stated that had the Japanese had seasoned pilots in those birds at the end of the war, many B29's would not have even made it to their targets.

Keep in mind, I'm a die hard P47 fan, but I have to give props to the Japanese for making a beautiful plane. It was faster and more maneuverable than the P51 at most altitudes and could almost keep up with the P47 until 22-25000ft. Then the P47 would take off again.