Busterbucani,
Stall speed increases with the square root of the load factor - I am sure that your error was just a typo! However, this is a simplified approximation that assumes that the lift curve slope remains constant at all speeds. In reality it does not. As Reynolds number (in essence TAS) increases, Cl max increases and thus the actual stall speed at greater than 1g is less than determined by the above relationship. This tends to be the case at low altitudes. However, as Mach number increases, Cl max reduces and so at high altitude the actual stall speed will be greater than the theoretical value calculated as above. This is also exacerbated by the fact that as altitude increases, the IAS for a given EAS increases. So, overall not as simple as you have implied.
My lack of comment as to the motion of the Gnat as shown in the videos is totally intentional! This is based on a few hours in the Gnat and significant experience of spinning and accelerated stalling in swept wing aircraft.