Pilots soon found themselves blacking out in turns tighter than they had ever imagined possible: the Spitfire was quite capable of pulling 10g in turns, an astonishing feat for 1940. Imagine what this meant: a 10 stone pilot pulling 10g would find his body weighing 100 stone, and this in age long before pressure suits. The Spitfire was also very fast. In April 1944, A Mk XI reconnaissance version flown by Flight Lieutenant 'Marty' Martindale reached 606mph in a 45-degree dive. This was just under Mach 0.9: the Spitfire was on its way to breaking the sound barrier before the propeller broke into pieces. Cool as a cucumber, Martindale lost height progressively in a controlled 20m glide, landing safely at Farnborough.
I stumbled across some excellent aircraft articles on the BBC this morning. This one on the Spitfire is well worth a read and has some beautiful pictures. Have a bonus video with the story of a Mark I that was shot down early in the war and recovered in the 1980's. It has since been restored to its original state and is apparently one of the few early examples left.