Okay John i've got the camera out...
Graph
Take a low AoB -
eg: AoB = 20 degrees, flaps up, MTOW, stall speed = 59 KIAS which
is equal to 57 * square root [1 / cos20 ]
Take a higher AoB -
eg: AoB = 60 degrees, flaps up, MTOW, stall speed = 87 KIAS which
is not equal to 57 * square root [2]