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Well, your eminent BoB historian had better get his facts straight, that or cut out the bias.
I have no idea but please see WWII Aircraft Performance
For British tests done at the time and pay attention to the conditions or engine limits (rpm and boost) used during the tests. Please note that the supercharger is geared directly to the crankshaft so the supercharger on a Merlin III will turn 848.8 rpm less for every 100 rpm of the engine which is why the boost tapers off so much while climbing vs the boost available at 3000 rpm in level flight ( you also have the ram effect in the inlet)
See WORLD WAR 2 FIGHTER GUN EFFECTIVENESS for some of the information on the guns, a lot of the rest can be found on internet fairly easy and just divide rates of fire and ammo capacity with a calculator.
Th bf109 could enter a dive quicker (perhaps much quicker) but that doesn't mean it was actually faster or that it was as controllable in a dive. That means aileron response and/or elevator response.
I have no idea of his of motive but the facts are there for anybody to check,
The fact that the Germans could get enough of a lead to escape from the Spitfires and Hurricanes by "bunting" into the dive while they had to roll before they could follow also answers a question earlier in the thread about the quickest way into the dive.
I'm sure there are plenty of occasions where a 109E was outclimbed, outfought or outdived by Hurricanes (let alone Spitfires) due to the pilot not manipulating his propeller properly in a life-and-death struggle.
To explain why a Bf 109 could enter a dive quicker than a Spitfire of BOB vintage, you have only to note the Bf 109 was fuel injected and the Spitfire was carbureted. If the aircraft were pushed over into a dive (called a "bunt" at the time), the carb would cough when under negative g and the Bf 109 would not, so it appeared to accelerate away. In fact, the Merlin soon revived when in the dive and The Bf 109 rapidly got to a speed where the controls were almost frozen. The main operational solution was to half-roll and THEN dive.
The Bf 109 was medium-speed dogfighter and was not very well-mannered above 400 mph, which was easy to reach in a full-power dive. And that's not a knock on the Bf 109 (surely a great plane). Rather it is a statement of the well know high-speed characteristics of the type. As I've said in here before, the very late-model Bf 109s, if they were going 450 mph, were running TO a fight or FROM a fight, but they weren't fighting at that speed; they were flying in a straight line and covering some serious ground. The best dogfight speeds for the Bf 109 series ranged from 180 mph to something just under 300 mph. They weren't bad at all from 280 to 320 or so mph, but they got pretty stiff above 350 mph and were almost unmanerverable above 400 mph, though they COULD get to that speed.
The inventive Tilly Shilling invented a small orifice (another name for a restrictor) that could be placed inside the carb to mitigate if not eliminate the negative g stuttering of the Merlin. It was called "Miss Shilling's orifice" or "Tilly's orifice" by the crews at the time. By 1943 the Merlin had a Bendix-Stromberg pressure carburetor that injected fuel at 5 psi. Later, the 100-series Merlin got an S.U. injection carburetor that injected fuel into the supercharger using a fuel pump driven as a function of crankshaft speed and engine pressures, effectively meaning it had fuel injection.