"Advantages of the P-51:
-Range big time
-Good rec plane
-Damn raids deep in enemy territory was b/c it had such range and very good speed.
-It was available in large numbers
- Decent armament on it.
Some not so great traits:
- Ok maneuverability only
- Not as tuff as the P-47, admittedly not many planes were.
- I have heard many times from unbiased reports that it could be tricky to handle at times, but over all pretty good.
But over all put all those + facts and very small - facts into one plane and you are right you have a pretty good plane. But if you could ever get that sort of range out of a Spit I would take a Spit over a P-51 anytime. What made the P-51 dangerous was its speed, range and numbers. But it is over rated to a degree."
The P-51 at high speeds was no slouch in the turn fight. But that aside, the P-51 achieved a great overall speed (cruise and top speeds both being high), exceptional fighter vs. fighter armament and easily flown. This is what we both agree on.
Rating the P-51 survivability as a negative point is a little unfair, as you point out it wasn't as tough as the P-47 but nothing much was. Compared to the other inline fighters of the era, the P-51 had no disadvantages worth mentioning.
If the P-51 didn't have it's legendary range, it would have provided an above average plane for actions down low. The RAF used the Mustang Mk.I and IA extensively over Northern France before deep penertrations were being made by the Allison cousins; Mustang Mk.IIIs started them. Pairs or trios of cannon armed Mk.IAs could provide a nasty surprise for the Luftwaffe when they were training or lining up to intercept a bomber formation early in the morning. The speed of the Mustang let it in and out of Axis Europe quickly, the Luftwaffe had a difficult time intercepting this small incursions. The 2nd TAF Mustangs achieved quite the success flying missions that could have been covered by the Spitfires range.
The real niché of the P-51 was it's range, we all know that. The 2nd TAF used the Mustang III with great success on early morning raids against enemy airfields in Germany. These were another shock to the Luftwaffe, they never expected to see six Mustangs dive-bombing German bases in Germany before the Allies were on the continent! Nothin' like puttin' on your Lieder-Hosen in the mornin' and hearing six Merlins roaring overhead!
A lot of people mistake the Mustang for being "relegated" to the armed-recon role by the RAF. But the Mustang was ordered for this role, to free up the Spitfire for the air superiority role. This provided a great partnership between the Spitfire and Mustang that is rarely mentioned. A great, and efficient sight to see, Mustang IIIs escorting "Bombphoons" while Spitfire IXs fly high over them. And these Mustangs weren't in a 10:1 situation against the Luftwaffe, like their USAAF brethren were.
We don't need to mention the role of the P-51 in the escort duties for the USAAF bomber streams, it's known by everyone.
The role of the Mustang as a war winning weapon is not over-rated. People will say the P-38 could have filled that role, but it didn't. The Mustang carried the bombers on it's shoulders to Berlin and beyond, then home again. The technical ability of the Mustang in a dogfight is the over-rated part, but be careful and don't instantly assume the Mustang was useless in one on one combat - pilots have many a wonderful story to tell!
That said, if they managed to get Spitfire Mk.IXs with the range of the Mustang while keeping every other ability. I would take the Spitfire Mk.IX everytime - but again, they didn't get anything like that into service.