I am talking about the best sustained turn rate, that is the best turn rate that can be maintained indefinitely without loss of speed, and that is usually what is referred to as "out-turning" or "matching turns" in WWII lingo because the target often had to be peppered steadily from a fixed distance, leading slightly accross a circle, for quite a while before going down from an average 2% hit rate.
High closure rates in straight dives, or brief snapshots, were more demmanding on the pilot's aiming skills, and more suited to less common centralized armaments or really fast-firing and flat-shooting guns.
The sustained turn rate has nothing to do with "Corner Speed", which was a concept defined after the war, and is the minimum speed at which maximum safe G can be reached. (During the war, this was typically referred to as the "minimum radius of turn" for 180° for a given starting speed followed by speed decay, as opposed to "out-turns" or "best turn rate" for full indefinitely sustained consecutive 360s)
In WWII "Corner Speed" would typically be the minimum speed to reach 6Gs, and that is emphatically NOT a sustainable turn rate...
In any case, even the more modern concept of "Corner Speed" is poorly understood in vintage WWII fighters: A 1989 "Society of Experimental test Pilots (SETP) evaluation of four US WWII fighter types (P-51D/P-47D/F4U/F6F-5) revealed the 6 G "corner speed" on all to be an extremely high 320 MPH IAS in flat level turns, or close to their maximum level speed at 10 000 ft....
Previous calculations assumed this was around 240-270 MPH, but 6 G at METO power could not be reached in level turns at these speeds without stalling, yet this apparenty can be done in dive pull-outs at reduced power...
In any case, the results were not what they expected, and it makes me wonder how the "well defined" limits of these types were actually tested, particularly with what instrumentation, especially regarding the in-flight wing-bending in level turns.