On the subject of turning.
Wing loading is an important indicator.
However it is not the only thing going on.
Unless somebody can explain how the Typhoon, with its higher wing loading has a slower stall speed?
I am not claiming the Typhoon can out turn the P-40 but the difference between them might not be as bad as the wing loading alone would suggest.
Now for sustained turning, each airplane has a combination of speeds and turn radius it can sustain over long periods of time while neither losing speed or altitude. Some planes can turn much harder (smaller radius) but only at the cost of bleeding off speed until the plane stalls or by doing a spiraling decending turn.
Planes with higher climb rates usually have more power/energy to fight this speed loss without having to lose altitude.
I would note that a Spitfire I might have lucky to sustain a 3 g turn at 10,000 ft without losing altitude and that is at speed well under 300mph.
We all know that a Spit mkI can turn much tighter than 3 Gs. It just can't do it at high speed or without losing altitude.
The 109E happened to be worse.
Hope that explains things.
Spitfire I through V was one of the most tight turning fighters of the War, only the Japanese fighters and the biplanes could out turn them and not all of those.
Most turning fights in WW2, and even some with Jets in later eras, descended downward over time if they continued to turn. Turning for a really long time though might not be necessary, for example it only took two "circuits" for a P-40 to get on the tail of a Bf 109 in typical circumstances, according to several Russian and Australian pilots anyway and I suspect a Spit could get on the tail of any German plane quicker than that. Depending on E states a 109 might have an advantage initially, in which case for example flaps might come into play* and both aircraft could end up in a descending spiral.
Turning is for a lot more than a sustained fight. It's an asset which can be used offensively and defensively - if for example a plane is making a pass at you, one of your options is you can turn sharply to throw off their shot - especially if they are faster they won't be able to pull lead - or turn into them to go head to head in a game of chicken**. Conversely if you are chasing, a better / tighter turning circle allows you to pull lead faster and thus get your shot off more quickly which is very important in air combat (so you can shoot him before his wing man gets you for example).
However if a P-40 is outnumbered like in the anecdote I posted from Lt Mobbs, he can't
keep turning long enough to get a shot as he'll probably have to reverse his turn to deal with the next attack. It becomes a game with each side pushing their luck. This is also another example of why roll is so important because you may instantly need to switch from turning right to turning left in that situation, and I think it's one of the two reasons why the Hurricane wasn't really viable as a fighter after 1941 but the P-40 was still in the game well into 1944.
By the way, I don't know if anyone cares but one common tactic used by the very successful 325th Fighter Group in the Med, and specifically over Sardania in a few battles where they seriously owned Italian and German fighters, was to send in an initial attack as bait, the latter would dive away from contact, 'pulling' pursuers under a second group which would dive down to get them. The 'bait' would then heave into tight banking 180 degree turns and join the fight. Mayhem ensued.
* for the P-40, Spits didn't have those kind of flaps settings probably because they didn't need them
** common tactics against Ki-43, A6M, Bf 109 and MC 202 but you wouldn't want to try that against a Fw 190 or a Typhoon