Whopity.
Not my understanding.....
A true Max rate turn is flown at the minimum speed needed to achive the limiting airframe load factor. You need to be flying at sufficient speed to pull maximum G without stalling, but no faster - which is around Va. I believe the maths supports this.
Typically, I understand that this requires a descent as there is unsually insufficient power in your usual training aircraft to maintain the limiting load factor in a level turn.
Regarding a minimum radius turn, thats where I most confused, although I don´t think it can be just ´slowest speed nessesary´as theoretically, the slowest you can go is just above the stall and put any reasonable bank on at that speed and you drop out of the sky. You must surely need to fly at a speed that allows you to fly at a reasonable angle of bank.....otherwise you are not going to turn.