I actually did an absolutely beautiful one, in a FIGHT no less, in a P-39D. Was knife fighting some guy in a Hurri-2C, had about 270 degrees on him but we were in a flat turn to the left (was before the flaps patch)... I knew I was a dead man, so I relaxed my turn and got my speed up to about 180 mph. He finally got around on me, doing about 130 or so I'd guess... I pulled up, went completely vertical, held in right rudder as I was about to stall and went over in a neat hammerhead, pretty as you please.
First and only one I've ever done.