That is one of my issues with the Pony... it seems that the majority of kills are really just picks. That works when you are in a supporting as cover for an attack element, but that's about all I can do with it. There really doesnt seem to be many times where I've felt like my skills have much of a contribution to the kill.
The P51 excells at speed. a pick is considered by many as shooting an enemy that is engaged. others see this as helping a fellow member out. So "picking" may not be the best word for it. P51s also do very well with flaps. one or two notches can really pull a tighter corner to get that annoying plane just out of your gunsight but dont feel uneasy about kicking full flaps in some situations. It may feel awkward fighting at low alts also but it is doable. i have killed many a foe who believed that a low pony = easy kill.
The 51 also does well if you maintain E by going vertical at times while on the deck. say after you shoot at a zeke low on the deck, you then pass by pull up and aim for your next target before coming back down (dont hang yourself unless you are safe or maybe a picker will come in and rip your wing off) etc. SA is also very much needed in these situations as you ARE in a vulnerable situation in a P51 low. It IS all relative to the situation of course.
P.S. The 51 has some quirky maneuvers that if you learn, will save your life many times. I had an I-16 and a KI-84 call for help while they were both on my six by pulling one of said maneuvers. The 84 ended up being shot up in the end. Dont be afraid to overuse elevator in extreme situations creating gyros and flatspins (and when i say extreme i mean extreme or you WILL most likely die).
Also like i said. SA is needed in general. Good SA=Longer lasting sorties. SA+ACM= many kills and quite possibly landing with them.