The comparison to a helicopter is a useful point, especially if it can match the turn rate with lower Gs.
But in this case, the the Gs are lower because the helicopter is in effect rotating on itself, continuously changing its directional axis inwards into the turn, which relieves the Gs experienced: Gs are from the trajectory vs speed alone, but if you rotate on yourself as you turn, this "extra fake turn rate" rotation -gained with the foot pedal I would assume- will gain you "turn" rate at no cost in Gs, as the pivoting is within your own CG: This feels like "nothing" in effect...
Except by working-in some momentary slip with the rudder, an aircraft cannot fly like that in continuous uninterrupted turns where maintaining speed at the highest possible sustained turn rate is paramount (side-slipping continuously would cause drag).
So my assumption, in the Finnish Me-109G pilot's case, is that if he claims to beat in turns aircrafts flying around in a flat circle (near the ground) at full or near-full power and 200-220 mph, pulling say 3.2 Gs, and he can beat that by going at an extremely slow speed of only 160 mph at partial power, then that means he is sustaining, all things being equal, at least 3.3 Gs at partial power and 160 mph, while the other can only sustain 3.2 Gs without losing speed, which his faster plane could not tolerate.
If the two aircrafts are assumed equal (the Finnish pilot considered his own aircraft's inherent turn rate to be inferior, given the extra weight/drag of two optional underwing 20 mm gondola guns weighting 180 lbs each, the sole performance difference in his mind being his continuous "downthrottling" tactic, with no mention of "upthrottling" ever), how can the other aircraft be threathened with a stall at 200 mph and 3.2 Gs (Quote: "He made a mistake and his aircraft warned, forcing him to widen his turn momentarily") while he himself, on an inferior aircraft, is not stalling at partial power, 160 mph, and yet gaining slightly at say 3.3 Gs in this apparently inferior state?
I do know about gravity-aided turns, but here, as in many WWII dogfights, the two are barely hanging on in consecutive flat turns: Gravity-aided turns have no relevance to sustained speed turns in level turns.
It seems to me there is no way an aircraft can match turn rate while actually pulling lower Gs, even if it is going slower: For an aircraft, a given sustained turn rate means a given amount of Gs: x degrees per second of turn rate means X Gs, no matter what the speed is.
Yes at lower speeds you can turn tighter than at high speeds, but you can only complete turns faster because you produce more degrees per second and at the same time more Gs.
My problem with what the Finnish pilot (27 kill ace Karhila) is saying is that basically, while being barely 50 mph above stall, he could still pull more sustained Gs than a faster flying aircraft, which, at 200 mph (40 mph faster than him) one must assume was closer to its "Corner Speed", since the corner speed on these things was measured as being in the 300 mph range, at that height, in 1989, by the SETP.
None of these fighters at the time had the power to sustain turns at their Corner Speed, so one would assume (for these old machines) the more power the better for the available sustained turn rate and thus available Gs at low speeds
So by lowering power away from his Corner Speed, he was mysteriously gaining slightly in his wing's available lift it seems, since he could produce more degrees per seconds on an inherently inferior-turning aircraft.
A quote might be useful to show I do understand the concept of "Corner Velocity": From "The art of the kill"
Corner Velocity
KCAS — knots, computed airspeed
You may think that slowing down to minimum airspeed and pulling as hard as you can is the best course of action in order to achieve a high turn rate. Not so fast. There is a relationship between airspeed and Gs. At lower airspeeds, you have less G available or, in other words, you can't pull as many Gs as you get slow. Less lift is produced by the wings of an aircraft at slower speeds, and as a result, there is less force available to turn the aircraft. If you get going really fast (above Mach 1, for example), you also lose G availability. For every fighter, there is an optimum airspeed for achieving the highest turn rate. The airspeed where the jet has the quickest turn rate with the smallest turn radius is called corner velocity. In most modern fighters, it is between 400 to 500 KCAS. The F-16 has a corner velocity of about 450 KCAS.