[Holtzauge]

The additional data posted by IvanK now gives the engine power as well and the turn time at 20,000 ft can as MIG-3U points out be read out of that figure to be in then order of 30 s. In fact the same report contains an even more precise figure of radius 1045 ft, bank angle 51 degrees and turn time 31.5 s in table 4 on page 4.

While we are waiting for Crummps 21 s 68 degree bank proof here are some C++ simulation results showing the relative performance between the 1.3 ata Me109E and Spitfire Mk1 at +6.25 boost:

As expected the Spitfire is somewhat better at 20,000 ft due to the lower wing loading. However, the interesting thing is however that at low level (1 km) my simulations show that while the Spitfire turn better at low speeds, the Me109E turns better than the +6.25 boost Spitfire Mk1 at TAS speeds over 290 Km/h. However, if one assumes the +12 boost then it is of course no contest, either at low or higher speeds.