I teach flat-flat. Actually, I prefer a rolling contact on the last step. What was the population they were looking at (men or women, elite vs sub-elite, etc.)?
I've found that the flat footed penultimate permits greater lowering of the COM in front of the foot. I would think that there is a slight tradeoff in velocity because of it (due to the deviation in normal mechanics) but it seems to me that it's one worth taking.
ELITETRACK Founder