To speed or not to speed...
There are couple of things at play here, already touched on but important none the less. The summation being what tools do you have and when / how to use them.
Speed: Speed in the WW2 fighter world comes from (for the most part) two sources or a combo of them. Those being aerodynamics and power. I'm not getting into the which prop is better, just looking at the power as stemming from the prop, engine, fuel as a group. The P-51A was noticeable faster than it's Allison counterparts due to some serious attention to aerodynamic details. Side benefits being better fuel milage (if there is such a thing in a WW2 fighter), better acceleration and maybe better high speed handling, higher critical mach, and or higher ceiling. All tools.
Power: Bill touched on it, but the power available versus required. His example being, "So, if a P-51B-1 and Bf 109G6 at 25K are zipping along at the 109's max Power/top speed of say 390mph, the 109G6 is way behind the 51B-1 in Energy available when the 51 pilot moves from MP to WEP." In any situation if you have more power available than the guy you are fighting you have a tool he doesn't. Doesn't mean you will use it correctly, at the right time, or in the right place, it just means it's there.
Maneuverability: While the Zero had tremendous range, it also had serious maneuverability advantages over it's Allied adversaries. If you can do something in a turning fight noticeably better than your adversary it is an advantage (and or tool) to be used against him or his type.
Speed has it's uses in WW2. If you are going fast enough it seriously impedes or reduces the ability for the adversary to complete an intercept (and shoot you down). If you are offensive it allows you to avoid attacks, as well as opens opportunities for you to attack that your adversary doesn't have. If you get bounced (tapped in todays terms) it might give you an opportunity to roll over and exit the fight (bandit not in range but in the attack mode) do to your higher speed / faster acceleration) or it might slow down his intercept enough that you can drag him / the fight over in front of a friend who can then put your bandit out of action. It's also usable if you are able to exit a turning fight (engagement in todays terms) before he can bring his nose to bear on you to shoot (or employ in todays terms). This is a difficult one as you are using your eyes / experience to judge the distance and are betting with your life. If he starts to shoot, you can jink (bullet avoidance maneuver), turn back in, or continue.
Power, or excess is a good thing. There are predominately two types of dog fights (BFM / Basic Fighter Maneuvers) and those are rate or radius fights. Rate is how man degrees of turn you can sustain over time (generally longer ranged fights), versus the radius fight (closer ranged fights in which the gun could be used also called a nose position fight) which is how many degrees can you turn over the next few seconds. Excess power if used correctly will keep you out of a short range fight. Or it will give you an advantage in a close fight if used correctly. I have fought F-18's with the Eagle, and they are much more maneuverable than I was. However, if we got into a groveling match, I would try to work the fight into the vertical since I have more power than he does. Get above him, open distance between you (aka turning room), then drop down while bringing the nose to bear so as to employ weapons. Also in a longer range fight, against an F-4, F-5, Mirage, F-16 (depending on it's configuration), if the guy can't shoot me then I'm going to play the rate game as it made for a longer life span. Same goes in WW2. If you are in a rate fight (trying to turn more degrees per second over time), you need to keep your speed up. An example is a guy attempts to shoot you, overshoots and his nose is stuck in lag (not able to bring it into lead due to your turning and his performance). You keep your speed up at or towards best rate speed, and maintain that while watching him. If he starts sliding from the back of your canopy towards the front he is losing that fight so don't change what you are doing if the fight allows (does he have a buddy about to jump you, does gas allow). Over time (unless he changes the fight) you will reel him in to arrive at his 6 o'clock with overtake ready to employ / shoot. If he elects to low yo-you shortly after over shooting (over rotate or dig under) then all you have to do is over rotate to keep him near the horizon (your perspective) and he will probably not get to a gun employment opportunity. That last maneuver will build angles between you, hopefully allowing for an separation (exit of fight).
Hopefully not too much detail. We look at the charts and they tell us a tremendous amount, but only at that one slice of time. We have seen where one airplane will have an advantage over another yet still lose. It could be the pilot didn't have the required situational awareness, or he lost sight for a moment, and loses in the end. Better plane, lesser plane, it doesn't matter if you don't use it well. In the case of the P-51BCD versus the Fw-190D-9 they seem very well (evenly) matched until you add in the Mustang flew from England, fought for 30 minutes, then flew back.
The big picture is speed, maneuverability, range, weapons, the pilots skill, are all tools. Use them better than your adversary, even if he has advantages, and you should be successful.
Cheers,
Biff