First heard about Kittenger in the 1999 6-part BBC/A&E series The Planets ( http://www.imdb.com/title/tt0283775 ) Amazing stuff. The story featured him performing in his bipe when introducing him.
I loved the way he explained how he stepped of the porch of the gondola and felt weightless, but wasn't moving. He then looked up and saw the gondola darting straight up at an incredible rate.
Of course, the reality was Kittenger was free-falling and the gondola was sitting essentially still. He would have initially barely felt any airflow over himself until he reached a significant true airspeed, roughly ten times his indicated airspeed (dunno if he had an ASI without more research.)
In the last year I ended up learning a bit about high-altitude flying myself through hobby-experimenting with X-Plane's simulated Mars environment ( http://www.youtube.com/watch?v=HJuD1wBJfjw ) Although a videogame, it does take into account density altitude. Nowadays, as is well known, there's a number of pilots on duty for the armed forces and civilian research projects seated relatively cozy somewhere near 0' AGL at a remarkably consistent 1G, flying UAV's, some of which operate at 60,000' AGL or higher.
Mars is about the equivalent of 80,000' MSL to 120,000' MSL or more Earth-density-altitude, from what I understand. (one source that addresses its lapse rate is http://www.grc.nasa.gov/WWW/K-12/airplane/atmosmre.html ).
"Sea-Level", so-to-speak, is around 0.27 inHG at 0' MML (Mars-Mean-Level). The floor of Valles Marineris is about -15,000' MML to -10,000' MML per the MOLA team at Goddard from the Pathfinder/MGS mission that returned digital-elevation-model data in the late 90's. I corresponded briefly with Gregory Neumann of the team a few years back. The Coronae low area in the southern hemisphere has the thickest air, around -24,000' MML.
Kittenger paved the way for many.
Greg Long - EAA #412965 + Ch 105 member