Hal- Glad to know that you model all your thoughts on what Ryan Hall does.
Hal and Coach G- Correct, leaning forward FROM THE HIPS is not conducive to higher knee drive. But having a forward lean from the ankle has very little effect on knee lift, unless you are trying to emulate sprint mechanics. However, we are addressing making this guy maintain better form for longer, which is about improving mechanical efficiency. Carrying the arms higher, while staying close to the body, creates a shorter & quicker pendulum and uses more of the stretch reflex, thus lowering the energy cost of moving the arms.
Additionally, bringing the arms up high(er) in front helps to rotate the hips to a more neutral pelvic. This tucked pelvis is what creates the higher knee drive. Trying to achieve this positioning of the hips is the same reason why you do not want to lean forward from the hips. Coach G, yes, the anterior core strength (psoas engagement) is very crucial in maintaining this as well.
You may feel the same effect on the hips by an upright posture but let me reiterate what i said about using gravity to its fullest extent...the higher arm carriage raises the center of gravity so a smaller amount of lean can create more forward momentum then your low arm carriage, upright alternative. Therefore, the overall efficiency is increased. And, yes, posterior chain (core) strength is needed to maintain this lean without bending at the waist.
I believe we are basically arguing the same things about pelvic tilt but we are using different means to achieve it.
And to Halitosis, if you would like me to point out some examples let me advise you to check out K Bekele, Haile G. and Eliud Kipchoge. Please note: none run like Ryan Hall. And if you have speed goggles, i think you know who is faster.
for some high-res photos:
http://www.olympic.org/kenenisa-bekele