Flight Journal
In the August 2003 issue, Flight Journal asked test pilot 'Corky' Meyer to choose the best fighter of WW2. It's a long article, which I'm not going to repeat here, but his ranking for the European theatre was:
1. P47
2. FW190
3. Spitfire/Seafire
4. P51
5. Yak1/Yak9
6. Bf109
7. P38
In his conclusion, he provides some stats for the P47, P51 and P38 and points out that "the P47 flew twice as many sorties, dropped 2,010% more bomb tonnage, destroyed 62% of the enemy's aircraft in the air and 75% on the ground and suffered only 58% of the losses per sortie of the P51"
For the Pacific theatre his rating was more predictable (as a renowned Grumman test pilot):
1. Hellcat
2. F4U Corsair
3. Zero
Not sure this counts as a 'learned opinion' but I hope it helps!
It's interesting that you rate the P51 as the better fighter. What criteria are you applying?