The P51 was an icon of the war. It's strengths are long range, high altitude, it's relatively fast, it turns well, good ammo load, can carry a good bomb load. It may not be the best at anything, but it is good at just about everything. In the MA, most the fights are low and you don't have to travel far for a fight. There are other planes that are much better for the fights in the MA.
The P51 is a fun plane to fly. Make sure you have time to gain some altitude (10K+). The plane does not have good guns for B&Z (no cannons). Try energy fighting. Energy fighting is is not B&Z. Your shots should be tracking shots from your enemys rear. You need to keep your fire on one point for a few seconds to do damage. Keep your speed high, don't turn tight with your enemy, break off and do a low energy (low G) turn and engage again.
If you get slow, use one notch of flaps and turn fight. If your enemy has no friends around, our you have a good wingman, you may get a kill and exit the area without being killed
Gunner