The speed required to pull 6 gs is the same. The difference between level or descending is how long you can sustain it with gravity helping.
So if corner is 320 that contradicts your minimum speed statement from earlier.
Also was the 320 the intersection of the accelerated stall and pilot g or airframe g limit?
No the horizontal and vertical "Corner Speeds" are
not the same: That is what the 320 MPH SETP 1989 test at METO
absolutely proves: When pulling out of a dive, the P-51D's 6G "Corner Speed" is 250 mph or thereabouts: That 70 MPH discrepancy (with modern 1989 instruments) absolutely proves that the vertical tolerates a lower speed for 6 G than the horizontal, which in effect proves the propeller's load influences the wingloading.
Hence the WWII obsession with down-throttling...
SETP test was Minimum to reach 6 Gs at METO.
"Corner Speed" is minimum speed to reach an unsustained 6 G, it has nothing to do with sustaining 3G turns "at a minimum speed"...
320 MPH for 6 Gs is so high the aircraft will barely maintain this 6 G for a few seconds...
The fact that the
horizontal corner speed is so close to max. level speed (and is at a much lower speed when pulling on the vertical) would mean that lowering power should
never help these things turn horizontally,
EVER, but it does... Hence the current basic knowledge is wrong on the horizontal (because they only ever took data from dive pull-outs -where the P-51D's Corner Speed is indeed around 240-250 mph-, dives during which the prop is unloaded).
It is the prop being loaded that skewers things (which doesn't happen nose-down), hence the down throttling for faster prolonged sustained speed horizontal turning, all the way down to 160 mph for the Me-109, as Karhila points out. Unloading the prop unloads the wings, allowing tighter sustained turns.
Gaston